GB2593895A

GB2593895A - Surgical implant procedures

Info

Publication number: GB2593895A
Application number: GB2005069.6A
Authority: GB
Inventors: O'connor Sean
Original assignee: Sean Oconnor
Current assignee: Sean Oconnor
Priority date: 2020-04-06
Filing date: 2020-04-06
Publication date: 2021-10-13
Also published as: GB202005069D0

Abstract

Measuring the inclination or vibration of a surgical instrument 24, (10, Fig 5) used in preparing for, or for effecting, implantation of a surgical implant 20. The instrument is preferably either an acetabular reamer (10, Fig 5) or acetabular cup inserter 24, and the surgical instrument an acetabular cup 20. The measurement is preferably undertaken using a sterile unit 38 that is removably attachable to the surgical instrument, the unit providing a housing in which an inclination sensor, such as an inclinometer, or vibration sensor is located. It can be inferred from the inclination measure whether correct orientation of the preparatory instrument (reamer) and acetabular cup has been achieved. A measure of vibration can be taken after impacting the acetabular cup introducer with a mallet (Fig 7(c)), with it being inferred from the vibrational measure whether correct and full implantation of the acetabular cup has been achieved. The data representing inclination and vibration may be remotely transferred to patient records with a time stamp as a way of verifying correct adherence to surgical procedure.

Description

Surgical implant procedures This invention relates to surgical implant procedures. The invention relates especially to the challenges associated with determining the correct placement of implants during surgery.

In principle, the invention could be used in a variety of surgical procedures. However, this specification will describe the invention in the context of orthopaedics, in particular hip replacement surgery, also known as hip arthroplasty.

The role of the hip joint in everyday activities is to support body weight and to maintain balance. For these purposes, the hip joint is a synovial ball-and-socket joint that rotates on more than one axis. The ball of the hip joint is comprised of the head of the femur, whilst the concavity of the socket is created by the acetabulum, which is a cup-like depression in the pelvic bone.

Movement can become limited when the hip joint experiences wear and tear. There are many reasons why bones or cartilage in the hip wear away, the most common being osteoarthritis. Osteoarthritis is a disease of the entire hip joint characterised by a breakdown of cartilage, bony change in the joints, inflammation of the joint lining and deterioration of tendons and ligaments. The hip may also be fractured in a fall or other accident, especially involving the elderly.

Hip replacement is a routine surgical procedure that is recommended when other options such as physiotherapy, exercise and medication are not effective. A typical hip replacement operation involves resurfacing bone and fitting the patient's body with the components required to create an artificial hip joint. Total hip replacement (THR) involves replacing both the acetabulum and the femoral head whereas a hemiarthroplasty involves replacing half of the hip joint, hence either the acetabulum or the femoral head but not both.

During THR, four parts are typically introduced to create a new hip, namely: an acetabular cup; an acetabular liner; a femoral head or ball; and a femoral stem. The cup and the liner together form the acetabular component of the new joint. Conversely, the head and the stem together form the femoral component of the new joint.

A typical THR procedure takes less than two hours, including administering anaesthetic. Indeed, it is common for less than half an hour to elapse between making the first incision and closing the incision to complete the procedure. In comparison to most surgical procedures, therefore, THR involves high patient turnover and creates a busy workload for surgeons, who could be called upon to perform the procedure several times a day.

Various hip replacement methods exist that differ slightly in practice. However, in general, the patient is immobilised on an operating table while under general or spinal anaesthetic. Once pre-operative procedures are complete, the hip is dislocated by pulling the ball of the femur from the socket of the acetabulum. The femoral head or ball is then resected and removed to gain access to the acetabulum or socket. The socket is then reamed to remove the damaged bone and cartilage, essentially resurfacing the socket while minimising the amount of excess tissue removed.

In this respect, Figures 1(a) and 1(b) show a reamer instrument 10 that comprises a body 12, a shaft 14 rotatable relative to the body 12 and a hemispherical reaming head 16 fixed to a distal end of the shaft 14. Figures 2(a) and 2(b) show the reamer instrument 10 in use, with the reaming head 16 spinning in the acetabulum 18 to resurface and hence enlarge the socket of the acetabulum 18.

The orientation of the reaming head 16 relative to the acetabulum 18 is important as the acetabular cup has to fit into the pathway that reaming creates. For this purpose, the surgeon assumes that the patient's pelvis is in a neutral position with respect to all three body planes at the time of implanting the acetabular cup, and hence also during reaming. Typically, surgeons use a freehand technique involving bone landmarks to estimate the best angle of orientation for reaming.

Figure 3 shows the next stage in the procedure, namely offering up a trial acetabular cup 20 to the reamed socket to gauge an appropriate cup size for the socket. The cup is at the distal end of a shaft 22 of an introducer instrument 24. A handle 26 at the proximal end of the shaft 22 is manipulated to pivot the shaft 22 and hence the cup 20 relative to the acetabulum 18, until the surgeon is satisfied that the cup 20 is oriented as required. In this example, an angle of 45° relative to horizontal or to the plane of the operating table 28 is appropriate, although a different angle may be chosen in other circumstances, for example if the patient exhibits pelvic tilt.

The angle of orientation of the acetabular cup 20 relative to the pelvis 30 is crucial to allow the patient a full range of motion and to avoid premature failure. In this respect, Figure 3 shows a conventional alignment guide structure 32 that is fixed to the shaft 22 of the introducer instrument 24 to provide a visual guide to the surgeon as to orientation. The guide structure 32 comprises an upright support member 34 fixed to the shaft 22 and a guide member 36 that extends on an axis orthogonal to the support member 34. The arrangement is such that the axis of the guide member 36 is horizontal, and hence parallel to the plane of the operating table 28, when the shaft 22 and hence the acetabular cup 20 are oriented at the desired 45°.

When an acetabular cup 20 has been selected to match the size of the reamed socket, that cup 20 can then either be cemented into the socket or uncemented with a press-fit into the socket.

Conventionally, the chosen acetabular cup 20 is fixed temporarily to the distal end of a shaft 22 of an introducer instrument 24, typically by complementary screw threads on the cup 20 and the shaft 22, such that the cup 20 is rotationally symmetrical about the central longitudinal axis of the shaft 22. Thus secured to the shaft 22, the cup 20 is seated gently into the acetabulum 18 and pivoted to the desired orientation. Orientation of the cup 20 may be determined by using a guide structure 32 like that shown in Figure 3 but is more commonly determined using the surgeon's own estimation. Next, when using the uncemented press-fit technique, the surgeon uses a mallet to strike the handle of the introducer instrument firmly and repeatedly until the cup is seated in the acetabulum at the required orientation.

When implantation of the acetabular cup 20 is complete, the shaft 22 of the introducer instrument 24 is unscrewed from the cup 20 to remove the instrument 24, leaving the cup 20 in place in the acetabulum 18. A bowl-shaped liner (not shown) is then inserted into the cup 20 to complete the acetabular component.

In THR, the next step involves broaching the femur to create a pathway for the femoral stem to be inserted. During broaching, a series of rasps or broaches of increasing sizes are inserted into the femoral canal to remove soft bone tissue until a firm fit is detected. Broaching is complete once the final broach is seated firmly in the femoral canal.

Typically the size of the femoral implant is chosen to match the size of that final broach.

A range-of-motion trial is then performed whereby a trial femoral head is placed on the final broach used and the limb is put through various ranges of motion to demonstrate stability. The size of the femoral head is selected to maintain stability and to match the size of the acetabular cup. Once attached, the femoral component is engaged with the acetabular component and the procedure can then be concluded by closing the incision.

As noted above, an essential aspect of a successful hip replacement procedure is correct positioning of the implant in the patient. Most commonly, the acetabular cup is optimally positioned at an inclination of between 400 and 45° relative to the plane of the operating table. If the implanted cup lies flush with a normal lateral pillar of the femoral head, the inclination angle is usually correct.

Correct positioning of the acetabular cup minimises wear during the initial bedding-in phase and later during the steady-state phase in use of the implant. However, if the acetabular cup is incorrectly positioned, this may result in a decreased range of movement, needless component wear, premature component failure and unnecessary revision surgery.

Thus, whilst THR is regarded as a straightforward and routine operation, surgical error can cause premature failure of an implant. The patient, the surgeon, theatre staff and medical device manufacturers all share an objective to avoid premature failure.

Correcting malpositioning of an implant in a revision procedure can cause substantial trauma to a patient as the surgeon must, in effect, dig out the implanted acetabular cup from the socket. This results in the socket becoming enlarged and misshapen, meaning that the surgeon must then ream the socket further. Thus, the socket will increase further in size and will require a larger cup, potentially leaving very little mantle of bone to work with should a further revision be required.

Enlarging the socket takes away more bone and so can weaken the pelvis; in any event, there may not be enough bone left to perform the procedure successfully. There is also the possibility of having to realign the stem of the implant to match the newly-implanted cup. These procedures cause the patient distress and discomfort and greatly extend the rehabilitation time.

Of course, failure of a surgical procedure can also expose a surgeon to litigation for clinical negligence. Surgeons rely on their own knowledge and experience to achieve best practice. Additionally, surgeons are burdened with making notes of each surgical procedure to specify what exactly was performed. Such notes can never be entirely complete or totally accurate, especially as there is no way of knowing for certain the exact conditions that prevailed during a surgical procedure. A lack of reliable evidence leaves surgeons vulnerable to an unfavourable outcome in litigation.

At present, surgeons use pre-operative templating in an effort to achieve optimal inclination. This technique guides the surgeon to the best-fit angle for implantation. The template is used in conjunction with the patient X-ray. However, patient x-ray scaling varies greatly from person to person. Therefore, pre-operative templating can only act as a rough guide for the surgeon and is not an accurate method of angle determination.

It will be apparent that the alignment guide structure 32 shown in Figure 3 is cumbersome and potentially inaccurate as it still relies on the surgeon's imperfect visual judgement. Also, the guide structure 32 only suits a preordained angle of orientation and cannot provide any useful guidance if the surgeon decides, during the procedure, that a different angle of orientation is appropriate.

Thus, the use of pre-operative templating and alignment guides is prone to human error and does not adequately address the challenges of performing arthroplasty. Due to a surgeon's busy workload, it is not uncommon for the surgeon to rely solely upon experience and intuition rather than separately verifying correct alignment. If the surgeon's estimate is inaccurate, this can accelerate premature failure or dislocation of the implant. Conversely, if the surgeon's estimate was in fact accurate, there is no proof that this was so.

Variation in patient anatomy can be problematic when assessing the angle of implantation. The optimal angle for patients suffering from conditions such as uneven hips or pelvic tilt may fall outside the aforesaid range of 400 to 45°. This is because the hip joint will be rotated or tilted to some extent.

As noted above, when the correct angle of implantation has been determined, the 35 acetabular cup must be secured in the acetabulum. When using the uncemented press-fit technique, the acetabular cup is impacted into position using a mallet. In this respect, the acetabular cup must be seated and engaged adequately with the acetabulum to enable new bone ingrowth. Therefore, sufficient mallet impaction is required to achieve correct and lasting positioning.

Another challenge of the procedure is that the surgeon has no way of measuring the amount of force applied to the mallet and hence to the pelvis via the acetabular cup.

This leads to a risk of the surgeon applying too much force, resulting in over-impaction and hence damage to the pelvis. Specifically, over-impaction can result in further bone loss, pelvic rupture or secondary fracturing. Conversely, under-impaction presents the risk of the acetabular cup failing to seat and engage adequately with the acetabulum.

As such, it is critical to seat the implant sufficiently but not to over-impact it.

O'Neill, Molloy, Patterson and Beverland, Orthopaedic Proceedings: "Digital Inclinometer-Assisted Acetabular Component Implantation: A Novel Technique to Improve Acetabular Component Orientation During Total Hip Arthroplasty' published online on 21 February 2018 acknowledges the problems associated with incorrect positioning of the acetabular component in patients. However, that paper does not consider the problems that the surgeon encounters with over-impaction or recording the correct performance of each procedure.

Conventionally, surgeons experienced in performing hip arthroplasty procedures understand that changes in the sound of the mallet strikes can provide a guide as to when the acetabular cup has been fully embedded in the acetabulum. In particular, there is a distinct change of tone with the final strike required to embed the acetabular cup. This tone change, in conjunction with visually witnessing the cup embedding, should indicate to the surgeon that no further strikes are necessary, or at least that any final confirmatory strikes should be made with less force.

In practice, however, the confirmatory change of sound may not be consistent from procedure to procedure and may not be heard clearly in a busy operating theatre. In any event, judging when to stop striking the mallet remains a subjective assessment on the part of the surgeon. Indeed, inexperienced surgeons might not even know what sound they are listening for. Again, this leaves the surgeon vulnerable to litigation if the outcome of the procedure is sub-optimal, especially in the absence of an objective record that the confirmatory sound was in fact heard.

Surgical procedures must of course be performed in sterile conditions. There is a need to ensure that each component brought into the operating theatre is sterile so as not to pose a risk of infection to the patient. Where possible it is preferable to employ single-use items in surgical procedures. Such single-use items save time and increase efficiency as they reduce the need for sterilisation procedures. However, a single-use approach can increase cost, especially where large or complex instruments have to be discarded rather than re-sterilised. Sterilisation presents particular challenges where surgical instruments contain electronic components, particularly if sterilising fluids are flammable.

Against this background, the invention resides in a surgical instrument for preparing for, or for effecting, implantation of a surgical implant, the instrument being fitted with a sensor that is configured to measure a positioning parameter being at least one of: inclination of the instrument; and vibration of the instrument.

The instrument may also be fitted with a display that is configured to display the positioning parameter(s). The sensor is preferably housed in a sterile unit that is removably attached to the instrument as an accessory to that instrument. Such a unit may also implement the display.

Where embodied in a removably attachable unit, the invention is apt to provide an accessory for a medical device as distinct from a medical device or instrument as such.

The significance of this distinction is that the accessory of the invention is not intended or designed to touch and interact directly with the patient; it is instead designed to attach to and to facilitate the use of an instrument that touches and interacts with the patient. This distinction is important and advantageous because an accessory avoids the heavier regulatory burden associated with medical devices and instruments.

A removably attachable unit of the invention may, for example, be clipped, clamped, bolted, strapped or magnetically attached to the instrument, or engaged with a complementary engagement formation of the instrument.

Conveniently, the sensor may be part of a handle module that is attachable to the instrument. The instrument may, for example, be a reamer for preparing an implantation site or an introducer for placing an implant at the implantation site.

The instrument may have a wireless transmitter for sending, to a remote receiver, data representing the measured positioning parameter(s). A memory may be provided for storing the data before transmission. A controller may be configured to time-stamp data representing the measured positioning parameter(s).

The inventive concept embraces a sterile unit that is removably attachable to a surgical instrument as an accessory to that instrument, the unit comprising a housing and at least one sensor within the housing that is configured to measure a positioning parameter being at least one of: inclination of the unit; and vibration of the unit. The unit may further comprise at least one display that is configured to display the measured positioning parameter(s).

A wireless transmitter within the housing may be configured to send, to a remote receiver, data representing the measured positioning parameter(s). A memory within the housing may store the data before transmission. A controller within the housing may be configured to time-stamp data representing the measured positioning parameter(s).

An internal power source may be sealed within the housing of the unit. An insulating tab may electrically isolate the power source from other internal components of the unit until being moved relative to the housing to connect the power source electrically to those other components. The insulating tab may be used to enable sterilisation of the unit to take place while minimising the risk of electrical current creating a hazard in conjunction with flammable sterilising fluids.

The inventive concept enables and extends to a method for determining positioning of a surgical implant, the method comprising measuring and optionally also displaying a positioning parameter of a surgical instrument that is configured to prepare for or to effect implantation, the positioning parameter being at least one of: inclination of the instrument; and vibration of the instrument.

Conveniently, at least one sterile sensor unit may be attached to the instrument and then may be used to measure the positioning parameter(s). The or each sensor unit may also be used to display the measured positioning parameter(s). The or each sensor unit may be provided in a deactivated state and then may be activated to measure the positioning parameter(s). For example, an internal power source may be electrically isolated from other internal components of a sensor unit in the deactivated state and may be electrically connected to those other components in an activated state Subsequently, the or each sensor unit may be detached from a first surgical instrument and then may be attached to a second surgical instrument to measure at least one positioning parameter of the second instrument. For example, the first instrument may be a reamer for preparing an implantation site and the second instrument may be an introducer for placing the implant at the implantation site.

After detaching a sensor unit from an instrument, that sensor unit may be discarded and the instrument may be sterilised.

Data representing the measured positioning parameter(s) may be transmitted wirelessly to a remote receiver, either in real time or after being stored. Any stored data may eventually be erased A time stamp and/or a device identifier code may be added to data representing the measured positioning parameter(s). In the latter case, after receiving the data, the device identifier code may be extracted from the data and matched with a patient record before the data is added to the patient record.

The method of the invention may comprise striking the instrument and measuring a vibration response of the instrument to being struck. The measured vibration response may be compared with a stored vibration response and an alert may be provided in case of a match with the stored vibration response.

When performed during an arthroplasty procedure, the method of the invention suitably comprises: measuring and displaying the inclination of an introducer instrument that supports an acetabular cup; and striking the instrument to implant the acetabular cup. The vibration response of the introducer instrument to being struck may also be measured and displayed. Preliminarily, the inclination of a reamer instrument may be measured and displayed while surfacing a pelvic recess to receive the acetabular cup.

To put the invention into context, reference has already been made to Figures 1(a) to 3 of the accompanying drawings, in which: Figure 1(a) is an exploded view of a reamer instrument comprising a reaming body, a shaft and a reaming head; Figure 1(b) is a side view of the reaming body, the shaft and the reaming head assembled together to form the reamer instrument; Figure 2(a) is a side view of the reamer instrument in use, reaming the acetabulum; Figure 2(b) is a perspective view showing the reaming head of the instrument engaged with the acetabulum; and Figure 3 is a schematic side view of an introducer instrument being used to align a trial acetabular cup in the reamed acetabulum, the introducer instrument being fitted with a conventional alignment guide for that purpose.

In order that the invention may be more readily understood, reference will now be made, by way of example, to the remainder of the accompanying drawings, in which: Figure 4 is a side view of a reamer instrument as shown in Figure 1(b) but adapted in accordance with the invention by the addition of a sensor unit that serves as an inclinometer and vibration sensor; Figure 5 is a side view of the reamer instrument of Figure 4 in use, reaming the acetabulum; Figure 6 is a side view of an introducer instrument adapted in accordance with the invention by attaching the inclinometer and vibration sensor unit shown on the reamer instrument of Figures 4 and 5; Figures 7(a) and 7(b) are side views of the introducer instrument of Figure 6 being used to align an acetabular cup in the reamed acetabulum; Figure 7(c) corresponds to Figure 7(b) but shows the introducer instrument being struck with a mallet to implant the acetabular cup in the acetabulum; Figure 7(d) corresponds to Figure 7(c) but shows a shaft of the introducer instrument being unscrewed from the now-implanted acetabular cup; Figure 7(e) is a side view of the introducer instrument from which the sensor unit has been removed to be discarded, allowing the introducer instrument to be sent for sterilisation; Figure 8 is an exploded view of a modular handle module in accordance with the invention in combination with separate inclinometer and vibration sensor units to be mounted in sockets of the handle module; Figure 9 is a side view of the handle module of Figure 8 fitted to a conventional reamer instrument like that shown in Figure 1(a); Figure 10 is a side view of the handle module of Figure 8 fitted to a conventional introducer instrument; Figure 11 is a side view of a variant of the handle module shown in Figure 8; Figure 12 is a side view of the handle module of Figure 11 fitted to a conventional reamer instrument like that shown in Figure 1(a); Figure 13 is a side view of the handle module of Figure 11 fitted to a conventional introducer instrument, demonstrating that the same modular handle can be used to attach sensor units to various instruments during a procedure; Figure 14 is a side view of an introducer instrument in a further embodiment of the invention; Figure 15 is a side view of an introducer instrument in another embodiment of the invention; Figure 16 is a side view of an introducer instrument in accordance with the invention comprising separate inclinometer and vibration sensor units; Figure 17 is a side view of a variant of the introducer instrument shown in Figure 16, comprising a combined inclinometer and vibration sensor unit; and Figure 18 is a block diagram of a sensor unit of the invention that implements inclinometer and/or vibration sensor functions.

Referring next, then, to Figures 4 and 5, a conventional reamer instrument 10 like that shown in Figure 1(b) is shown here adapted in accordance with the invention by attaching a discrete sensor unit 38 that comprises an inclinometer and optionally also a vibration sensor. For regulatory purposes, the sensor unit is regarded as an accessory for an instrument rather than as an instrument itself, and therefore is subject to a simpler regulatory regime.

The sensor unit 38 can be supplied to the operating theatre in sterile packaging and, in principle, could even remain within that packaging when in use. The sensor unit 38 is single-packed, pre-calibrated, powered up and immediately ready for use, if necessary after performing a simple activation step as will be described.

The sensor unit 38 may be attached in various ways and with various fixings, such as a modular housing, a magnet, a bracket, a fastening or a clip. In this example, the sensor 38 unit is attached to the reamer instrument 10 with a band or strap 40 that tightly encircles the body 12 of the reamer instrument 10 and may be fixed there with a hook-and-loop fastener or a closure such as a clasp.

The sensor unit 38 comprises a numerical inclinometer display 42 that indicates the inclination of the sensor unit 38 in degrees relative to the horizontal. Thus, by being fixed to the reamer instrument 10 in alignment with the central longitudinal axis of the shaft 14, the sensor unit 38 displays to the surgeon the inclination of the shaft 14 and thus of the reaming head 16. It is simple for the surgeon to see the inclination throughout, to adjust the inclination until a desired angle is reached and to maintain that angle during the reaming process as shown in Figure 5.

As will be explained later, the sensor unit 38 may have recording and reporting functionality to store and optionally to transmit data representing the inclination of the reaming head 16 during the reaming process, as well as the inclination of the cup 20 during implantation.

Turning next to Figures 6 to 7(e), these drawings show how a sensor unit 38 of the invention can also be used on an introducer instrument 24. Any convenient means of attachment may be employed, as noted above Conveniently, as in this example, the same sensor unit 38 can be re-used by being removed from the reamer instrument 10 and then being attached to the introducer instrument 24. Alternatively, the reamer instrument 10 and the introducer instrument 24 could each have their own respective sensor units 38. In that case, the sensor unit 38 of the reamer instrument 10 can be removed from the reamer instrument 10, after reaming, and discarded to allow the reamer instrument 10 to be sterilised for reuse.

In this example, the band or strap 40 of the sensor unit 38 is again tightly fastened around the introducer instrument 24, for example around the handle 26 of the introducer instrument 24 as shown here, and may again be fixed there with any suitable fastener or closure. Thus, by being fixed to the introducer instrument 24 in alignment with the central longitudinal axis of its shaft 22, the sensor unit 38 displays to the surgeon the inclination of the shaft 22 and thus of the acetabular cup 20.

Again, it is simple for the surgeon to see the inclination on the display 42 of the sensor unit 38 throughout and to adjust the inclination until a desired angle is reached. This is illustrated in Figures 7(a) and 7(b), where an initial estimated inclination of 55° to the horizontal is corrected to a desired inclination of 45° to the horizontal. The surgeon can then easily maintain the chosen inclination during the implantation process as shown in Figure 7(c), in which a mallet 44 is used to strike the handle 26 at the proximal end of the introducer instrument 24 to embed the acetabular cup 20 firmly in the acetabulum 18.

Once the acetabular cup 20 is fully embedded, the shaft 22 of the introducer instrument 24 is unscrewed from the cup 20 as shown in Figure 7(d). The sensor unit 38 may then be removed from the introducer instrument 24 and discarded to allow the introducer instrument 24 to be re-sterilised as shown in Figure 7(e).

As will be explained later, the sensor unit 38 may also have recording and reporting functionality to store and optionally to transmit data representing the inclination of the acetabular cup 20 during the implantation process.

The display 42, recording and reporting functionality of the sensor unit 38 may also extend to determining when the acetabular cup 20 is fully engaged within the acetabulum 18. This is the purpose of the aforementioned vibration sensor of the sensor unit 38. The vibration sensor is configured to sense and display one or more characteristics of the changing sound of successive mallet strikes, corresponding to vibration of the introducer instrument 24 as the acetabular cup 20 approaches full engagement within the acetabulum 18. Such characteristics may be expressed as the frequency, loudness or decibel change, tone or quality of the sound or vibration.

In this example, as best appreciated in Figure 7(e), the display 42 of the sensor unit 38 comprises a row of lights 46 that illuminate in response to the vibration sensor. The lights 46 illuminate during the implantation process in response to the changing sound of successive strikes of the mallet 44. The lights 46 may, for example, have traffic light colouring of green to continue mallet strikes with full force because the cup 20 is not yet embedded, amber to continue mallet strikes with reduced force because the cup 20 is nearly embedded, and red to stop mallet strikes because the cup 20 is now fully embedded. More generally, illumination of a succession of, say, one light, two lights and three lights 46 could provide a similar display function. Other visual and/or audible alerts as to the progression of the embedding process are, of course, possible.

It would be possible for the inclinometer of the sensor unit 38 to provide similar visual and/or audible alerts instead of, or in addition to, a numeric display 42, for example using a series of lights 46 which may have traffic light colours to indicate when the sensor unit 38 is inclined correctly or incorrectly.

Turning next to Figures 8 to 15, these drawings show various ways in which an inclinometer and/or a vibration sensor can be attached to or integrated with a surgical instrument in accordance with the invention.

Figures 8 to 10 show a handle module 48 having sockets 50 into which an inclinometer 52 and a vibration sensor 54 can be inserted. In this example, the handle module 48 has male screw threads 56 at each end that complement female screw threads (not shown) in the proximal end of a reamer instrument 10, as shown in Figure 9, and in the proximal end of an introducer instrument 24 as shown in Figure 10. Thus, the same handle module 48 can be used successively on the reamer instrument 10 and the introducer instrument 24, providing support for those instruments and allowing their inclination and/or vibration to be determined and displayed as appropriate.

Providing screw 56 threads at both of the opposed ends of the handle module 48 allows those threads to differ in size or pitch to suit different screw threads of the reamer instrument 10 or the introducer instrument 24. The handle module 48 can simply be turned around to present the appropriate thread 56 to the instrument in question. However, it would of course be possible for the handle module 48 to have a screw thread 56 at only one end if desired, or for the screw thread(s) of the handle module 48 to be female threads instead.

In this example, the inclinometer 52 or the vibration sensor 54 both have numeric displays. For example, the vibration sensor 54 may display a frequency that characterises the sound or vibration of successive mallet strikes and that therefore indicates to the surgeon the successive stages of the implantation process.

Advantageously, where the inclinometer 52 or the vibration sensor 54 have a numeric display 42, the display 42 flips upon inversion so that the numerals can always be read easily the right way up. For this purpose, the inclinometer 52 and/or the vibration sensor 54 may respond to an on-board accelerometer.

After use, the inclinometer 52 and the vibration sensor 54 can be removed from the handle module 48 and discarded so that the handle module 48 can be sterilised if desired. Alternatively, the handle module 48 could be removed and discarded along with the inclinometer 52 and the vibration sensor 54 if preferred. Thus, the inclinometer 52 and/or the vibration sensor 54 could be an integral part of the handle module 48 rather than being insertable into and removable from the handle module 48.

In this respect, Figures 11 to 13 exemplify a variant of the handle module 48 that comprises an integral inclinometer 52 and vibration sensor 54. In this variant, the screw threads 56 of the preceding embodiment are replaced by magnets 58 at one or both ends of the handle module 48. The magnets 58 allow the handle module 48 to be attached to the proximal end of a reamer instrument 10, as shown in Figure 12, and the proximal end of an introducer instrument 24 as shown in Figure 13.

Of course, magnetic fixings 58 like these could be applied to arrangements in which the inclinometer 52 and/or the vibration sensor 54 are insertable into and removable from the handle module 48 as in Figures 8 to 10. Again, where the inclinometer 52 or the vibration sensor 54 have a numeric display, the display may be arranged to flip upon inversion. However, a numeric display is not essential for either function and could be replaced or supplemented by other audible or visual alerts or displays as mentioned above.

Figures 14 and 15 show other arrangements for removably attaching sensor units 38 to introducer instruments 24. Similar arrangements could be used to attach sensor units 38 temporarily to reamer instruments 10. In these examples, the sensor units 38 have combined inclinometer 52 and vibration sensor 54 functionality but either of those functions could of course be omitted.

In Figure 14, the sensor unit 38 is clipped to the introducer instrument 24 with a bracket 60 that embraces the shaft 22 of the instrument 24. The bracket 60 may, for example, have resilience to enable a snap-fit connection or may be clamped around the shaft 22.

Conversely, in Figure 15, the sensor unit 38 is clamped to the introducer instrument 24 with a screw 62 that extends through the shaft 22 of the instrument 24 and is engaged by a nut, exemplified here by a wing nut 64. Of course, all elements required for attachment to an instrument 24 must be provided in sterile form.

Figures 16 and 17 show that sensor units 38 may be attached to or integrated directly into specially-adapted introducer instruments 24. Again, similar arrangements could be used to attach or integrate sensor units 38 in reamer instruments 10.

Figure 16 shows separate sensor units 38 providing inclinometer 52 and vibration sensor 54 functionality whereas Figure 17 shows a single sensor unit 38 with combined inclinometer and vibration sensor functionality 66. Again, either of those functions could be omitted. In these examples, the sensor units 38 are insertable into and removable from one or more sockets 50 in the handle 26 of the introducer instrument 24, enabling the sensor units 38 to be discarded while the remainder of the introducer instrument 24 is sent for sterilisation. After sterilisation of the introducer instrument 24, the sensor units 38 can be replaced with new, sterile, sensor units 38 so that the introducer instrument 24 is ready for re-use.

Turning finally to Figure 18, this diagram exemplifies the internal arrangement of a sensor unit 38 of the invention. The sensor unit 38 is manufactured to a medical-grade standard, hermetically sealed, with a shatterproof window protecting any display. The unit 38 is provided in a sterile form that is ready for use before, during and after implantation.

In particular, the sensor unit 38 has a sealed housing 68 that contains an on-board power source 70 providing electrical power to a controller 72 and to other components within the housing 68, namely: one or more sensors 74 for sensing inclination and/or vibration; one or more displays 76 for displaying the sensed inclination and/or vibration, and/or related alerts; optionally, a memory 78 for recording data representing the inclination and/or vibration of the unit 38 over time throughout the surgical procedure, for which purpose the recorded data may be time-stamped by a clock function of the controller 72; and optionally, a comms interface 80 for communicating the data to an external recipient such as the Cloud 82 or a nearby device such as a computer or a mobile telephone 84, conveniently via a radio or Bluetooth® connection.

The data representing the inclination and/or vibration of the sensor unit 38 over time through the surgical procedure may be communicated from the unit 38 in real time during the procedure or may be downloaded from the memory 78 after the procedure.

The data provided by the sensor unit 38 enables an independent record to be created to confirm that the reamer and introducer instruments of the preceding figures were indeed being held at the desired inclination. The data also enables an independent record to be created to confirm that the introducer instrument vibrated in a manner consistent with correct seating of the acetabular cup in the acetabulum.

By combining the data sets representing inclination and vibration, it is possible to infer that the introducer instrument was correctly oriented at the moment of impaction and full engagement of the acetabular cup in the acetabulum. This confirms that the acetabular cup was correctly placed during the procedure and so helps to protect the surgeon and the implant manufacturer against any claims to the contrary.

To maintain data security when the sensor unit 38 has been discarded after use, provision may be made to wipe any data held in the memory 78 in response to an external signal, or in response to downloading the data or the lapse of a predetermined period of time.

Figure 18 also shows the option of an activating element for powering up the sensor unit 38 at an appropriate moment immediately before or during the procedure. In this example, the activating element is an electrically-insulating pull-out tab 86 that, in an isolating position as shown, isolates one or both terminals of a battery of the power source 70. This facilitates pre-use sterilisation of the deactivated sensor unit 38 with the battery already installed within the housing 68, without requiring the battery to be inserted after manufacture of the sensor unit 38 or requiring a large and difficult-to-seal opening to be provided in the housing 68 for insertion of the battery by a user.

In the isolating position shown in Figure 18, a free end of the tab 86 protrudes from a narrow, easily-sealed slot in the housing 68. This enables the tab 86 to be grasped and pulled out of the housing 68 to power up the sensor unit 38 by allowing the battery to connect electrically to the other components within the housing 68.

Thus, the sensor unit 38 does not require the insertion of a battery, is sterile-packed and is immediately ready for use. The tab 86 of insulating plastics not only satisfies sterilisation requirements but also maximises battery life. Additionally, whatever attachment fixings are required for the sensor unit 38 may be presented as a sterile selection that is ready for use in accordance with the surgeon's preference. The sensor unit 38 can then be placed on existing hospital instruments without having to use or add further instruments that require sterilisation, washing and storage. The sensor unit 38 may be used at various times during a procedure and may be attached to various instruments during a procedure. The sensor unit 38 may confirm or record numerous orientation angles throughout the procedure and not just the angles outlined above.

As the battery life of the sensor unit 38 need only be long enough to serve a single procedure, the battery can be small and inexpensive. A small, single-use battery is safe to discard within the unit 38 when the procedure has been completed.

Many variations are possible within the inventive concept in addition to those mentioned above. For example, a sensor unit of the invention may have in-built algorithms to help a surgeon to deal with various abnormalities that may be encountered in arthroplasty procedures, such as pelvic tilt, limb length discrepancy or pelvic deformity. A 10° pelvic tilt, for instance, would require a math calculation so as to achieve the end result of a 45° inclination of the cup. Thus, the unit may be capable of integrating angle adjustments to achieve a target orientation. As such, the sensor unit can facilitate complex cases where custom angle adjustment is required to achieve maximum range of motion in the patient.

Each sensor unit may have a stored reference identifier pertaining to a single procedure. This identifier can be used to record and prove the orientation angles measured by the unit during that procedure in addition to data confirming correct impaction of the implants. The identifier of the unit can correspond with, and be matched externally to, the ID of the patient held in hospital records. This ensures that no confidential patient data needs to be stored in or transmitted from the unit.

A sensor unit of the invention may incorporate additional sensing technology within the same housing, with the ability to detect and measure parameters such as time elapsed or theatre temperature during the procedure. This data can be used to confirm procedure outcomes such as blood loss, bone abnormality or leg length anomalies.

In this respect, procedural information such as blood loss currently has to be determined and written into patient notes. Aided by its simple numerical display and supplemented by an input interface such as a voice recorder, the accessory of the invention could be used as a measuring and input device whereby such information can be measured or entered and then communicated directly to patient notes.

Compared with the alternative of the surgeon recording this data by hand or dictating it to be typed up later, this saves time and improved accuracy.

Infection detection sensors may also be incorporated to show the presence of an infection pre-and post-operation. For example, infection control based on conventional colour-change technology could be incorporated on or into the housing of the unit to be recorded and date-stamped.

Claims

Claims 1. A surgical instrument for preparing for, or for effecting, implantation of a surgical implant, the instrument being fitted with a sensor that is configured to measure a positioning parameter being at least one of: inclination of the instrument; and vibration of the instrument.
2. The instrument of Claim 1, wherein the instrument is also fitted with a display that is configured to display the or each positioning parameter.
3. The instrument of Claim 1 or Claim 2, wherein the sensor is housed in a sterile unit that is removably attached to the instrument.
4. The instrument of Claim 3 when dependent upon Claim 2, wherein the unit also implements the display.
5. The instrument of Claim 3 or Claim 4, wherein the unit is clipped, clamped, bolted, strapped or magnetically attached to the instrument.
6. The instrument of any of Claims 3 to 5, wherein the unit is engaged with a complementary engagement formation of the instrument.
7. The instrument of any preceding claim, wherein the sensor is part of a handle module that is attachable to the instrument.
8. The instrument of any preceding claim, being a reamer for preparing an implantation site or an introducer for placing an implant at the implantation site.
9. The instrument of any preceding claim, fitted with a wireless transmitter for sending, to a remote receiver, data representing the or each measured positioning parameter.
10. The instrument of Claim 9, fitted with a memory for storing the data before transmission.
11. The instrument of any preceding claim, fitted with a controller that is configured to time-stamp data representing the or each measured positioning parameter.
12. A sterile unit that is removably attachable to a surgical instrument, the unit comprising a housing and at least one sensor within the housing that is configured to measure a positioning parameter being at least one of: inclination of the unit; and vibration of the unit.
13. The unit of Claim 12, further comprising at least one display that is configured to display the or each measured positioning parameter.
14. The unit of Claim 12 or Claim 13, further comprising a wireless transmitter within the housing for sending, to a remote receiver, data representing the or each measured positioning parameter.
15. The unit of Claim 14, further comprising a memory within the housing for storing the data before transmission.
16. The unit of any of Claims 12 to 15, further comprising a controller within the housing that is configured to time-stamp data representing the or each measured positioning parameter.
17. The unit of any of Claims 12 to 16, further comprising an internal power source that is sealed within the housing.
18. The unit of Claim 17, further comprising an insulating tab that electrically isolates the power source from other internal components of the unit and that is movable relative to the housing to connect the power source electrically to those other components.
19. A method for determining positioning of a surgical implant, the method comprising measuring a positioning parameter of a surgical instrument that is configured to prepare for or to effect implantation, the positioning parameter being at least one of: inclination of the instrument; and vibration of the instrument.
20. The method of Claim 19, comprising also displaying the measured positioning parameter.
21. The method of Claim 19 or Claim 20, comprising attaching at least one sterile sensor unit to the instrument and then using the or each sensor unit to measure the or each positioning parameter.
22. The method of Claim 21 when dependent upon Claim 20, comprising also using the or each sensor unit to display the or each measured positioning parameter.
23. The method of Claim 21 or Claim 22, comprising clipping, clamping, bolting, strapping or magnetically attaching the or each sensor unit to the instrument.
24. The method of any of Claims 21 to 23, comprising engaging the or each sensor unit with a complementary engagement formation of the instrument.
25. The method of any of Claims 21 to 24, comprising attaching the or each sensor unit to the instrument as part of a handle module that is attached to the instrument.
26. The method of any of Claims 21 to 25, comprising providing the or each sensor unit in a deactivated state and then activating the sensor unit to measure the or each positioning parameter.
27. The method of Claim 26, wherein an internal power source of the or each sensor unit is electrically isolated from other internal components of that sensor unit in the deactivated state and is electrically connected to those other components in an activated state.
28. The method of any of Claims 21 to 27, comprising subsequently detaching the or each sensor unit from a first surgical instrument and attaching the or each sensor unit to a second surgical instrument to measure at least one positioning parameter of the second instrument.
29. The method of Claim 28, wherein the first instrument is a reamer for preparing an implantation site and the second instrument is an introducer for placing the implant at the implantation site.
30. The method of any of Claims 21 to 29, comprising subsequently detaching the or each sensor unit, discarding the or each sensor unit and sterilising the or each instrument.
31. The method of any of Claims 19 to 30, comprising wirelessly transmitting, to a remote receiver, data representing the or each measured positioning parameter.
32. The method of Claim 31, comprising transmitting the data in real time.
33. The method of Claim 31, comprising storing the data before transmitting the stored data.
34. The method of Claim 33, comprising erasing the stored data.
35. The method of any of Claims 19 to 34, comprising adding a time stamp to data representing the or each measured positioning parameter.
36. The method of any of Claims 19 to 35, comprising adding a device identifier code to data representing the or each measured positioning parameter.
37. The method of Claim 36, comprising: receiving the data; extracting the device identifier code from the data; matching the device identifier code with a patient record; and adding the data to the patient record.
38. The method of any of Claims 19 to 37, comprising: striking the instrument; and measuring a vibration response of the instrument to being struck.
39. The method of Claim 38, comprising comparing the measured vibration response with a stored vibration response and providing an alert in case of a match with the stored vibration response.
40. The method of Claims 19 to 39 when performed during an arthroplasty procedure, the method comprising: measuring and displaying the inclination of an introducer instrument that supports an acetabular cup; and striking the instrument to implant the acetabular cup.
41. The method of Claim 40, comprising the preliminary step of measuring and displaying the inclination of a reamer instrument while surfacing a pelvic recess to receive the acetabular cup.
42. The method of Claim 40 or Claim 41, comprising measuring and displaying the vibration response of the introducer instrument to being struck.