Introduction

Traditional TKR designs exhibit abnormal and unpredictable kinematics: with posterior subluxation in extension and anterior slide with flexion. These can contribute to restricted knee flexion and reduced quadriceps efficiency. Newer designs attempt to provide “guided motion” with the aim of mimicking normal knee kinematics. The Journey (Smith & Nephew) BCS TKR incorporates both an anterior and a posterior cam/post mechanism while Triathlon PS TKR (Stryker) incorporates a posterior cam/post mechanism. This study compares the in-vivo kinematics of these two designs and compares it with normal knee.

The heat produced by drills, saws and PMMA cement in the handling of bone can cause thermal necrosis. Thermal necrosis could be a factor in the formation of a fibrous tissue membrane and impaired bony ingrowth into porous prostheses. This has been proposed to lead to non-union of osteotomies and fractures, the failure of the bone-cement interface and the failure of resurfacing arthroplasty.

We compared three proprietary blades (the De Soutter, the Stryker Dual Cut and the Stryker Precision) in an in-vitro setting with porcine tibiae, using thermocouples embedded in the bone below the cutting surface to measure the increases in bone temperature.

There was a significant (p=0.001) difference in the change in temperature (δT) between the blade types. The mean increase in temperature was highest for the De Soutter, 2.84°C (SD: 1.83°C, range 0.48°C to 9.30°C); mean δT was 1.81°C (SD: 1.00°C, range 0.18°C to 4.85°C) for the Precision and 1.68°C (SD: 0.95°C, range 0.24°C to 5.67°C). Performing paired tests, there was no significant difference in δT between the Precision and Dual Cut blades (p=0.340), but both these blades had significantly (p=0.003 for Precision vs De Soutter, p<0.001 for Dual Cut vs De Soutter) lower values for δT than the Dual Cut.

It is established good practice that hip and knee replacements should have regular follow-up and for the past seven years at the North Hampshire Hospital a local joint register has been used for this purpose and we compare this with results of the Swedish and UK national and the Trent Regional registries.

Since March 1999, all primary and revision hip and knee arthroplasties performed at North Hampshire Hospital, Basingstoke have been prospectively recorded onto a database set up by one of the senior authors (JMB). Data from patients entered in the first five years of the register were analysed. All patients have at least one year clinical and radiological review then a minimum of yearly postal follow-up. 3266 operations (1524 hips and 1742 knees) were performed under the care of 13 consultants. Osteoarthritis was the most common primary diagnosis in over 75% of hips and knees. Our revision burden was 7.5% (10.2% hips and 3.5% knees). As of 31/12/2006 6.2% of patients had died and 5.5% were lost to follow-up.

Revision rates were 1.5% and 1.4% for primary total hip and knee replacements respectively.

Our data analysis of revisions and patello-femoral replacements has allowed us to change our practice following local audit which is ongoing. Oxford scores at 2 years had improved from a mean of 19 and 21 pre-operatively to 40 and 39 for primary hips and knees respectively. Our costs are estimated at approximately £35 per patient for their lifetime on the register.

Compared to other registries:

Our dataset is more complete and comprehensive

Our aim was to determine the effects of tibial component malrotation and posterior slope on knee kinematics following Scorpio cruciate retaining total knee replacement in cadaver specimens.

The movements of the hip, thigh and lower leg were monitored in 3D using a validated infra-red Computer Navigation System via bone implanted trackers. Ten normal comparable cadaver specimens were mounted in a custom rig allowing 3D assessment of kinematics under various loading conditions. The specimens then underwent Navigated TKR as per normal operating surgical protocols however an augmented tibial component was implanted. This allowed the researchers to precisely modify the rotation of the tibial component around its predetermined central axis, as well as to alter the posterior slope of the component. A pneumatic cylinder was used to provide a simulated quadriceps extension force while the knee was tested with a variety of applied loads including anterior and posterior draw, abduction and adduction, internal and external rotation.

TKR kinematics are significantly different from those of the native knee (p< 0.05). Increasing tibial posterior slope resulted in an incremental posterior position of the femur (p< 0.05), deviation of the neutral path of motion (p< 0.05) and alteration of the normal AP envelope of laxity (p< 0.05). Tibial component malrotations over 10 degrees resulted in increasing deviations of the neutral movement path of motion (p< 0.05) without significantly affecting the envelope of laxity. Tibial component malrotations of more than 10 degrees, when combined with a posterior slope of six degrees or more, resulted in prosthetic subluxation under certain loading conditions.

This study has demonstrated significant differences in knee kinematics before and after total knee implantation. Increasing values of internal and external rotation, as well as posterior slope of the tibial tray resulted in further deviations of total knee kinematics from normal by altering the neutral path of motion and the soft tissue envelope, with combined misalignments resulting in the greatest deviations from normal with prosthetic subluxation in some cases. Deviations from normal kinematics may result in increased ligament tension and incongruence or dysfunction of the component articulations, with the generation of sheer forces in the gait cycle. These may contribute to premature wear and loosening. Surgeons should be aware of this when considering the addition of posterior slope or assessing tibial component positioning in TKR.

Aims: To determine the effects of tibial component rotation and posterior slope on kinematics following Scor-pio navigated TKR in cadaver specimens.

Methods: Knee kinematics were monitored using a validated Infra Red Navigation System. Ten normal comparable cadaver specimens were mounted in a custom rig allowing assessment of kinematics under various loading conditions. The specimens then underwent Navigated TKR. The surgery was performed as per normal operating surgical protocols by an expert knee surgeon. However an augmented tibial component was implanted allowing the researchers to precisely modify its rotation and posterior slope. A pneumatic cylinder attached to the quadriceps tendon was then used to repetitively flex and extend the knee with a variety of applied loads.

Results: Kinematics were different after TKR. Increasing posterior slope resulted in increasing posterior position of the femur, particularly at maximum flexion. Posterior slope also resulted in a deviation of the neutral path of motion and alteration of the normal envelope of laxity. Tibial component malrotations over 5 degrees resulted in deviations of the neutral path of motion without affecting the envelope of laxity. A combined malrotations over 10 degrees with posterior slopes over 6 degrees resulted in prosthetic subluxation under certain loading conditions.

Discussion: Knee kinematics are different after TKR. Increasing internal and external malrotation as well as the addition of posterior slope resulted in deviations of TKR kinematics through alteration of the neutral path of movement and or the envelope of laxity. Combined misalignments of slope and rotation resulted in the greatest deviations from normal kinematics and in some cases, prosthetic subluxation. Incompatibilities of alignment may result in increased ligament tension and component articulation dysfunction that may contribute to premature wear and loosening. Surgeons should be aware of this when considering the addition of posterior slope or assessing tibial component positioning in TKR.

AIMS: To determine the effects of tibial component rotation and posterior slope on kinematics following Scorpio CR navigated TKR in cadaver specimens.

METHODS AND RESULTS: Knee kinematics were monitored using a validated IR Navigation System. Ten normal comparable cadaver specimens were mounted in a custom rig allowing assessment of kinematics under various loading conditions. The specimens then underwent Navigated TKR. The surgery was performed as per normal operating surgical protocols by an expert knee surgeon. However an augmented tibial component was implanted allowing the researchers to precisely modify its rotation and posterior slope. A pneumatic cylinder attached to the quadriceps tendon was then used to repetitively flex and extend the knee with a variety of applied loads.

Kinematics were different after TKR. Increasing posterior slope resulted in increasing posterior position of the femur, particularly at maximum flexion. Posterior slope also resulted in a deviation of the neutral path of motion and alteration of the normal envelope of laxity. Tibial component malrotations over 5 degrees resulted in deviations of the neutral path of motion without affecting the envelope of laxity. Combined malrotations over 10 degrees with posterior slopes over 6 degrees resulting in prosthetic subluxation under certain loading conditions.

Discussion: Knee kinematics are different after TKR. Increasing internal and external tibial component malrotation as well as the addition of posterior slope resulted in deviations of TKR kinematics through alteration of the neutral path of movement and or the envelope of laxity. Combined misalignments of slope and rotation resulted in the greatest deviations from normal kinematics and in some cases, prosthetic subluxation. Incompatibilities of alignment may result in increased ligament tension and component articulation dysfunction that may contribute to premature wear and loosening. Surgeons should be aware of this when considering the addition of posterior slope or assessing tibial component positioning in TKR.

Background: Several approaches to the ACL attachment and drilling methods exist, with little evidence of which method is the best.

Hypothesis: The “Retrodrill” or an “inside-out” drilling technique result in uniform intra-articular tunnel mouths compared with standard “outside-in” conventional ACL drill bits.

Study Design: Controlled laboratory study.

Methods: Sixteen cadaveric knees were divided into Anterograde (A) and retrograde “Retrodrill” (R) groups and ACL tunnels drilled. The femoral tunnel mouths were moulded using PMMA, then Nylon rods of identical diameter containing 1mm diameter K-wires were inserted into the tunnels and AP and lateral X-rays taken. Matching laboratory experiments utilised 10 pig femurs and synthetic bone.

Results: In group A, the mean difference between tunnels and their mouths was 1.6±0.5mm, compared with 0.3±0.2mm for Group R (p < 0.001). The mean femoral tunnel angulation in the sagittal plane for Group A was 45±10 degrees and 78±14 degrees for Group R (p< 0.001); and 30±12 degrees, and 71±12 degrees (p< 0.001) in the coronal plane respectively. There were similar ACL attachment hit rates from the groups. In porcine bone, tunnel mouth widening in the anterograde tibial group was 0.7±0.4mm, 0.04mm±0.1mm for the anterograde femoral group, and 0.06±0.1mm for the retrograde group (p< 0.001). In synthetic bone, the difference between the tunnels and their mouths was 0.8±0.8mm, 0.2±0.1mm and 0.1±0.1mm (p< 0.001) respectively.

Conclusions: The “Retrodrill”, or an inside out antero-grade drilling technique, produced a more uniform tunnel with no difference in ACL attachment hits.

Introduction: The cam-post mechanism of Posterior Stabilized Total Knee Arthroplasty (PS-TKA) should provide a constraint that limits anterior translation of the femur on the tibia in flexion and thereby ensure femoral roll-back with progressive knee flexion. In a previous fluoroscopic study we showed that the sagittal plane kinematics of a PCL substituting TKA (Scorpio PS) was abnormal in flexion, suggesting inefficiency of the cam-post mechanism. We also assessed the movement of the femur relative to the tibia using the Patella Tendon Angle (PTA) through the range of knee flexion (0 to 90 degrees). The aim of the current study was to investigate in greater detail why the cam-post mechanism was ineffective by assessing the contact point movement and the distance between the cam and post.

Method: Twelve patients with Scorpio PS TKA underwent fluoroscopic assessment of the knee during a step up exercise and a weight bearing deep knee bend. The image distortion was corrected using a global correction method and the data was analysed using a 3D model fitting technique. Having determined the component position, the minimum distance between cam and post were determined. The femoro-tibial contact positions of the medial and lateral condyles were determined relative to the mid-coronal plane of the tibial component. The PTA was calculated by measuring the angle subtended by patella tendon with the tibial axis and was plotted against knee flexion angle (KFA).

Results: The relationship between PTA and KFA was abnormal relative to the normal knee. Between extension and 60 degrees flexion there was forward movement of both medial (11 mm) and lateral (5 mm) femoral condyles. Thereafter, both condyles moved back (10 mm). The cam-post mechanism failed to engage in one case while in others it engaged between 70 to 100 degrees.

Conclusions: The 3D analysis has confirmed the preliminary findings of the previous study using the PTA and KFA relationship. Despite the cam engaging in flexion normal knee kinematics were not restored. The femoral roll-back is inadequate and starts to occur at least 20 degrees before the cam and post engage.

Introduction: Total knee replacement (TKR) is a common treatment for end stage osteoarthritis of knee. The best knee replacement is one in which the kinematics of the normal knee are reproduced. Amongst several factors affecting kinematics, variation in surface geometry and the retention/ sacrifice of the PCL are considered especially important. It is not known which of these two factors is most influential for establishing optimum joint kinematics after TKR.

Method: Four groups of patients who had undergone TKR at least one year previously were recruited. Two groups of patients had undergone replacement with a single axis design (Scorpio, Stryker Howmedica) in both PCL retaining (Scorpio CR, n=15) and PCL sacrificing (Scorpio CS, n=15) variants. The other two groups had undergone replacement with the traditional polyradial design prosthesis (Sigma, Depuy, Johnson & Johnson), again with both PCL retaining (Sigma CR, n=14) and PCL sacrificing (Sigma CS, n=13) variants. An in-vivo fluoroscopic analysis was carried out on all patients. Patients were asked to perform closed chain step up and open chain extension and flexion against gravity. The kinematic profile of each knee was obtained by measuring patella tendon angle (PTA) at specific angles of knee flexion (KFA) using an established fluoroscopic method. The data was also compared with the kinematic profile of normal knees. American Knee Society, Oxford and Patella Scores were recorded for all patients.

Results: All groups were comparable in terms of age and gender. In addition, no significant difference was found between groups in clinical outcome. PTA results for a step-up exercise are shown in the figure. A one way ANOVA between groups revealed that knee kinematics after total knee replacement is different to that for normal knees. No differences were found between groups when the data was analysed using CR/CS as the independent variable. The only differences between groups were found when surface geometry was used as the independent variable. It was shown that the kinematic profile of the single axis Scorpio design (in both CR & CS ) was closer to normal, especially near extension, than the traditional polyradial design (Sigma CR & CS).

Conclusions: Kinematics after a total knee replacement differ from that for a normal knee. Differences in surface design between knee replacements appear to have greater influence on kinematics than the presence or absence of the PCL.

Purpose The tensile strength of the isolated Medial Patellofemoral Ligament (MPFL) is unknown. The strength required of reparative or reconstructive procedures to re-constitute this major patella stabilising structure are therefore unknown.

Method 10 fresh cadaveric right (6 female 4 male) knees, mean age 71.6 (SD 16.6) years, were prepared to isolate the MPFL between the patella and the Medial Femoral Condyle (MFC). The tensile strength and mode of failure were then determined.

The ligament was then repaired using a suture and the tensile strength of this determined. The ligament was then reconstructed in three ways including: Biodegradable corkscrew anchors and two tendon techniques with interference screws. One method used a blind tunnel into the MFC, while the other passed through a tunnel in the femoral condyles. Both methods passed through tunnels in the patella.

Results The mean ultimate tensile strength of the isolated MPFL was 207.9 (SD 90.1) Newtons. Seven specimens failed through a mid-substance tear while three pulled off the MFC.

The mean strength of the suture repair was 36.7 (SD 26.5) Newton. The biodegradable bone anchor gave a mean strength of 142.3 (SD 38.5) Newton. The blind tunnel hamstring reconstruction’s had a mean strength of 126 (SD 20.8) Newton. The double tunnel hamstring reconstruction’s failed at a mean of 195.0 (SD 65.6) Newton.

Conclusion The force required to rupture an isolated MPFL appears to be approximately 210 Newton. Suture repair is insufficient to reconstitute this. Reconstruction with bone anchors or hamstring tendon techniques come close to this.

Introduction: Unicompartmental knee arthroplasty (UKA) is an increasingly popular procedure for young osteoarthritic patients whose age and activity levels preclude the use of a total knee arthroplasty (TKA). However, successful reconstruction using an unconstrained mobile bearing implant requires an intact and functioning ACL. Patients with isolated medial compartment OA and an absent ACL therefore provide a management dilemma for the treating surgeon. One option is to perform a combined ACL reconstruction and mobile bearing UKA. This paper presents early results of this new procedure using an Oxford UKA and ACL reconstruction using an autograft.

Materials and Methods: Eleven patients who underwent one or two-staged ACL reconstruction and Oxford UKA for treatment of symptomatic medial compartment OA were reviewed at one year after surgery. The combined procedure required specific precautions and considerations; care had to be taken to place the tibial tunnel as far laterally as possible to avoid impingement of the graft by the tibial implant. Also, the presence of a posteromedial, rather than an anteromedial cartilage defect has the potential to reduce accuracy for placement of the initial tibial cut.

Results: All patients were male with an average age of 49 years (range: 36 – 52) and mean follow up of 1.3 years. One patient needed revision to TKA due to infection. The objective and functional knee society scores improved pre to post operatively from 55 to 98, and 85 to 100, respectively.

Conclusions: ACL reconstruction and simultaneous or staged UKA is a viable treatment option for patients with symptomatic medial compartment arthritis in whom the ACL is absent. Early results of this technically demanding procedure are encouraging but longer follow-up is required.

Introduction: The aim of this study was to compare two methods of femoral fixation for four strand Hamstring (4SH) primary ACL reconstruction: namely a recently introduced suspensory fixation using absorbable polylactic acid cross pins versus our traditional method of anchor fixation.

Method: Forty-five consecutive patients, who had undergone primary ACL reconstruction using 4SH graft and the suspensory femoral fixation were prospectively evaluated by an independent observer. IKDC scores were recorded and laxity was assessed using cruciometer. These results were compared with a similar well-matched cohort of patients whose femoral fixation was with an anchor. Tibial fixation in both the groups was similar.

Results: No significant difference was noted between the two groups on comparison of IKDC scores or cruciometer readings at a minimum one-year follow-up.

Conclusions: This suspensory method of femoral fixation for a four-strand hamstring graft provided a secure fixation with satisfactory early clinical results. As this method of fixation is a new technique, further follow-up is needed for long-term validation.

Aim: To compare the kinematic profile of two types of TKRs – a single-axis design Vs a polyradial design, with that of the normal knee.

Methodology: An in-vivo fluoroscopic analysis was carried out as part of a four-armed prospective randomised trial comparing the clinical outcome of two commonly used types of TKRs each with posterior cruciate retaining -CR and sacrificing –CS models. The kinematic profile was obtained by measuring patella tendon angle at specific angles of knee flexion using an established fluoroscopic method whilst the patients performed close and open chain exercises. The data was compared with the kinematic profile of the normal knee.

Results: Fifty-five patients who had undergone TKR at least one year prior, were invited to take part in this ethically approved study. They were matched for age and gender and had a similar clinical outcome.

The kinematic profile of single axis design TKR was closer to normal especially near extension. During mid-flexion, abnormal anterior femoral translation was noticed with the polyradial design. No significant difference was noted between CR and CS designs.

Conclusions: Kinematics after a TKR differed from that of a normal knee. Reproducible differences were found between the two designs, which may predict mode of failure and longevity.

Introduction: Number of patients needing revision ACL surgery has increased more than 10 fold. Results of revision surgery are traditionally thought to be inferior to primary reconstruction. Aim of this paper is to describe results of revision surgery using a two-stage technique and compare it with results of primary ACL reconstruction. Materials and Methods: We studied 44 consecutive patients with revision ACL surgery. They had 10 ACL reconstruction elsewhere using autologous (34) or prosthetic ligament (10). Rrevision surgery was two staged. First of debridement and bone grafting and second stage after 3 mths of meniscal and chondral work along with ACL reconstruction using autograft. We compared this group with a similar cohort of patients with primary ACL surgery. Conclusions: A two-stage revision technique for revision ACL surgery allows accurate assessment & opportunity for the bone graft to heal to provide good bed for graft fixation at the time of second procedure.