Abnormal sagittal kinematics after total knee replacement (TKR) can adversely affect functional outcome. Two important determinants of knee kinematics are component geometry and the presence or absence of a posterior-stabilising mechanism (cam-post). We investigated the influence of these variables by comparing the kinematics of a TKR with a polyradial femur with a single radius design, both with and without a cam-post mechanism.

We assessed 55 patients, subdivided into four groups, who had undergone a TKR one year earlier by using an established fluoroscopy protocol in order to examine their kinematics in vivo. The kinematic profile was obtained by measuring the patellar tendon angle through the functional knee flexion range (0° to 90°) and the results compared with 14 normal knees. All designs of TKR had abnormal sagittal kinematics compared with the normal knee. There was a significant (p < 0.05) difference between those of the two TKRs near to full extension. The presence of the cam-post mechanism did not influence the kinematics for either TKR design. These differences suggest that surface geometry is a stronger determinant of kinematics than the presence or absence of a cam-post mechanism for these two designs. This may be because the cam-post mechanism is ineffective.

Polished, tapered stems are now widely used for cemented total hip replacement and many such designs have been introduced. However, a change in stem geometry may have a profound influence on stability. Stems with a wide, rectangular proximal section may be more stable than those which are narrower proximally. We examined the influence of proximal geometry on stability by comparing the two-year migration of the Exeter stem with a more recent design, the CPS-Plus, which has a wider shoulder and a more rectangular cross-section. The hypothesis was that these design features would increase rotational stability.

Both stems subsided approximately 1 mm relative to the femur during the first two years after implantation. The Exeter stem was found to rotate into valgus (mean 0.2°, sd 0.42°) and internally rotate (mean 1.28°, sd 0.99°). The CPS-Plus showed no significant valgus rotation (mean 0.2°, sd 0.42°) or internal rotation (mean −0.03°, sd 0.75°). A wider, more rectangular cross-section improves rotational stability and may have a better long-term outcome.

Purpose of the study Function is strongly infl uenced by proprioceptive ability, this prospective longitudinal study aimed to evaluate the change in proprioceptive performance after knee replacement; comparing total to unicompartment replacement.

Methods and Results Two groups of patients with OA as diagnosed clinically and by X-ray were recruited. Group 1 consisted of 15 patients (mean age 65.8yrs range 57-72yrs, 10 females & 5 males) listed for Total Knee Arthroplasty (TKA) with the AGC (Biomet, UK). Group 2 consisted of 19 patients (mean age 65.5yrs range 52–75yrs; 9 females & 10 males) listed for Oxford Uni-compartmental Knee Arthroplasty (OUKA) for medial compartment OA. The ACL and PCL were present and preserved in all patients in Group 2, while only the PCL was preserved for Group 1 patients.

Joint Position Sense (JPS) & sway were used as measures of proprioception performance. Both groups were assessed pre- and 6 months post-op. JPS was measured using an isokinetic dynamometer (KinCom, Chatanooga Ltd) as the error in actively and passively reproducing fi ve randomly ordered knee fl exion angles (30°, 40°, 50°, 60° and 70°). Sway (area, path and velocity) was measured during single leg stance using a Balance Performance Monitor (SMS Medical) for 30-second interval. Functional outcome was assessed using the Oxford Knee Score (OKS).

Pre-operatively, no differences in JPS or sway were found between limbs in either group. No differences existed between the two groups.

Post-operatively, both groups had signifi cant improvement of JPS in the operated limb only (Mean ± standard deviation for UKA 4.64±1.44° and for TKA 5.18±1.35°). No changes in JPS were seen in the control side. Group 2 patients showed signifi cant improvement in both sway area and path (p< .0001) for both limbs post-operatively. No signifi cant post-operative changes in sway occurred in either limb of Group 1 patients.

The OKS improved post-operatively in both groups, rising from 21.4 to 35.5 for Group 1 patients and from 23.9 to 38 for Group 2 patients.

Conclusion Interestingly, joint position sense improved for both groups but did not seem to show any difference between UKA and TKA. Postural sway was infl uenced by joint replacement type. Ligament retention may contribute to improved global postural control seen after unicompartmental knee arthroplasty and may explain the higher level of function seen in these patients.

Introduction: Oxford Unicompartmental knee arthroplasty (UKA) is now performed using a minimally invasive surgical (MIS) technique. Although early results are encouraging, the studies assessing outcome could be criticised for the restricted number of patients and centres involved. A multi-centre follow-up of patients is required to confirm the preliminary findings.

Aim: To examine early clinical outcome in patients with minimally invasive Oxford medial UKA using a multi-centre, multi-surgeon design.

Materials and Methods: This prospective study was carried out in three centres with involvement of six surgeons. All patients undergoing cemented Oxford UKA for medial OA using MIS were included. 231 consecutive UKAs with a minimum follow up of 2 years (mean: 2.84) were assessed using objective and functional Knee Society Score (KSS).

Results: There were 108 females and 102 males (21-bilateral) with average age of 66.8 years (42 – 86). No significant difference was noted between various age groups or between different surgeons. Three knees were revised: one for infection, one for unexplained pain and one for bearing dislocation. Cumulative survival rate at 2 years was 98.6% with 93% patients having good or excellent KSS rating.

Conclusions: This multi-centre study has confirmed preliminary findings that Oxford UKA using a minimally invasive approach is safe and effective.

The Birmingham hip resurfacing (BHR) arthroplasty is a metal-on-metal prosthesis for which no medium- or long-term results have been published. Despite this, it is increasing in popularity as an alternative to stemmed prostheses for younger patients. Since the fixation of the socket is conventional, the major concern is long-term failure of the femoral component. This can be predicted by the use of roentgen stereophotogrammetric analysis (RSA). We have therefore undertaken such a study of the BHR femoral component over a period of two years.

Twenty patients (22 hips) underwent a standard BHR procedure. Migration of the femoral component was measured by RSA at intervals of three, six, 12 and 24 months. At 24 months the total three-dimensional migration of the head was 0.2 mm. This was not statistically significant. Previous studies have shown that implants which loosen quickly have rapid early migration. Our results therefore suggest that the BHR femoral component is an inherently stable device which is likely to perform well in the long term.

Introduction: In conjunction with a bilateral randomised control trial comparing the clinical outcome of two total knee arthroplasties (TKA), we carried out an in-vivo fluoroscopic analysis of both knees in the trial. Knee A, is a new mobile bearing posterior cruciate retaining TKA and Knee B, an established fixed bearing posterior cruciate retaining TKA.

Method: In an ethically approved study, video fluoroscopy was taken of both knees of seven patients performing three exercises; extension against gravity, flexion against gravity and a step up exercise. Ten images at ten-degree intervals over the flexion range were frame grabbed and digitised. The relationship of patella tendon angle (PTA) to knee flexion angle (KFA) was assessed using a newly developed computer system. Five normal knees in fit volunteers were also fluoroscoped and assessed.

Results: A similar pattern of results was obtai ed for all three exercises. Knee A behaved in a linear, more consistent fashion than Knee B, which behaved non-linearly. Analysis of variance showed this difference was significant for all three exercises (p < 0.039).

Conclusions: This bilateral study provides a powerful way of assessing the kinematics of two different knee implants. Knee A behaves in a linear predictable fashion that is nearer normal than Knee B. These results will be used in conjunction with a clinical outcome study and an RSA study to provide a complete assessment of a new TKA.

This early study examines the influence of a wider shoulder on the 1 year migration of a cemented, polished, tapered stem, using RSA.

Polished, tapered stems (PTS) have excellent 10 year survival rates. RSA studies have demonstrated that these devices subside about 1 mm / year. Small amounts of subsidence are beneficial in stabilising a stem. Stem rotation (measured as posterior head migration) within the cement mantle is probably a more important mechanism of failure than subsidence. Stems with a wider proximal portion are thought to better resist rotation. The CPS (Endoplus, UK) is such a device; here we compare its’ stability with that of the Exeter.

20 patients received the CPS-plus stem and underwent RSA examinations at 3, 6 and 12 months postoperatively. The Exeter 1 year migration data was used as a comparison. Both groups underwent a Hardinge approach with CMW3G cement.

Both stems subsided about 1mm. The CPS showed less medio-lateral and A-P movement of the proximal stem than the Exeter over 1 year, as shown below:

The CPS internally rotates less than the Exeter, as demonstrated by the smaller amount of posterior head migration. It has a lateral flare of the shoulder; making its cross-section wider than the Exeter’s, this probably accounts for its’ greater resistance to rotation. The CPS also undergoes less medio-lateral proximal stem migration. Its’ lateral shoulder flare is probably responsible for this axial subsidence, as it prevents the shoulder from moving laterally whilst subsiding over the calcar.

A PTS with a broad proximal section is more stable, this may confer an increased survival advantage.

We have assessed the effectiveness of reconstruction of the anterior cruciate ligament (ACL) in reducing functional tibial translation (TT).

The gait of 11 ACL-deficient patients was studied using Vicon equipment before and after surgery. Measurements of the angle between the patellar tendon and the long axis of the tibia were obtained in order to calculate TT in the sagittal plane relative to the uninjured limb during standing and walking.

Before surgery, patients did not show abnormal TT on the injured side, but after surgery significant anterior TT was found in the operated limb for every parameter of gait.

Abnormal anterior TT occurring during activity does not seem to be reduced by reconstruction; rather, it increases. It may be that the increased translation results from relaxation of excess contraction of the hamstring muscles, since compensatory muscle activity no longer is required in a reconstructed knee. The reduction of TT may not be an appropriate objective in surgery on the ACL.

Studies using roentgen stereophotogrammetric analysis (RSA) have shown that the femoral components of cemented total hip replacements (THR) migrate distally relative to the bone, but it is not clear whether this occurs at the cement-implant or the cement-bone interface or within the cement mantle. Our aim was to determine where this migration occurred, since this has important implications for the way in which implants function and fail.

Using RSA we compared for two years the migration of the tip of the stem with that of the cement restrictor for two different designs of THR, the Exeter and Charnley Elite. We have assumed that if the cement restrictor migrates, then at least part of the cement mantle also migrates.

Our results have shown that the Exeter migrates distally three times faster than the Charnley Elite and at different interfaces. With the Exeter migration was at the cement-implant interface whereas with the Charnley Elite there was migration at both the cement-bone and the cement-implant interfaces.