Introduction and Aims: Single compartmental replacement procedures are increasingly preferred over total knee replacement (TKR) for single compartment osteoarthritis of the knee joint. Theoretically, reduced disruption of the native joint should produce more normal kinematics. This study aimed to describe and compare the sagittal plane kinematics of four different, commonly used devices.

Method: Four groups of patients who had undergone successful single compartment replacement at least two years previously were recruited. Fifteen following Oxford medial UKA, 12 following medial St Georg Sled UKA, five following Oxford lateral UKA, and 12 following Avon PFJ replacement. Patients performed flexion/extension against gravity, and a step-up during video fluoroscopy. The Patellar Tendon Angle (PTA), the angle between the long axis of the tibia and the patella tendon, was obtained as a function of knee flexion. This relationship provides indication of sagittal movement between femur and tibia through range and has been validated as a reliable measure of joint kinematics.

Results: The kinematic profile for each group was compared to that of the profile for 12 normal and 30 TKR (AGC) knees. All three tibiofemoral devices produced knee kinematics similar to the normal knee. The PTA was found to have a linear relationship to flexion angle, decreasing with increasing knee flexion angle. No such linear relationship exists for the TKR joint, which display abnormal kinematics. The PF device also reflected similar trends to that for normal knees except that the PTA was moderately increased throughout the entire range of flexion (three degrees).

Conclusion: In contrast to TKR, all single compartmental knee replacements provided kinematics similar to the normal joint. The kinematic pattern of the PFJ replacement may be of most interest as the observed increase in PTA through range could influence patello-femoral contact forces

When the Oxford unicompartmental meniscal bearing arthroplasty (UCA) is used in the lateral compartment of the knee 10% of the bearings dislocate. An in-vitro cadaveric study was performed to investigate if the anatomy and joint geometry of the lateral compartment was a contributory factor in bearing dislocation. More specifically, the study investigated if the soft tissue tension of the lateral compartment, as determined by the length of the lateral collateral ligament (LCL), was related to bearing dislocation. A change in length of greater than 2 mm is sufficient to allow the bearing to dislocate.

The Vicon Motion Analysis System (Oxford Metrics, Oxford, UK) was used to assess length changes in the LCL of seven cadaveric knees. Measurements were made of the LCL length through knee flexion and of the change in LCL length when a varus force was applied at a fixed flexion angle. Measurements were made in the normal knee and with the knee implanted with the Oxford prosthesis.

In the intact knee the mean LCL change was 5.5mm (8%) over the flexion range. After implantation with the Oxford UCA the mean change in length was only 1 mm (1%). There was a significant difference in the LCL length at 90° (p=0.03) and 135° (p=0.01) of knee flexion compared to the intact knee. When a varus force was applied the LCL length change of the intact knee (5.4 mm) was significantly different (p=0.02) to that of the knee with the prosthesis implanted (2.7 mm)

This study used a new method to dynamically measure LCL length. It found that after implantation of the Oxford lateral UCA the LCL remains isometric over the flexion range and does not slacken in flexion as it in the normal knee. This would suggest that the soft tissue tension was adequate to contain the bearing within the joint.

However, when a varus force was applied the LCL did not sufficiently resist a displacing force producing an LCL length change greater than 2 mm.

The evidence provided by this study is contradictory. The “lack of change in LCL length through flexion” suggests that the ligament remains tight through range and is unlikely to allow dislocation. However, the amount of distraction possible when an adducting moment is applied is sufficient to allow bearing dislocation. The length tension properties of the lateral structures are therefore implicated in the mechanism of dislocation.

Aim: In 1990 the Christchurch Hospital Sarcoma Clinic established management guidelines for patients with suspected sarcomas, recommending referral prior to investigation, biopsy and excision. The aim of this study was to determine whether these guidelines are being followed.

Method: A review of the case notes of all sarcomas referred to the Sarcoma Clinic between 1990 and 1999 was performed.

Results: There were 53 referrals, 34 (22%) from orthopaedic surgeons, 56 (37%) from general surgeons, 16 (10%) from general practice and 47 (31%) from other specialties. Only 83 (54%) of the referrals had followed the guidelines. Twenty-five (74%) of the orthopaedic referrals, 19 (34%) of the general surgical, 10 (63%) of the general practice and 29 (62%) of the other specialties had followed the guidelines. Seventy (46%) of the referrals had failed to follow the guidelines. Thirty-four (49%) of these had undergone excision inadequate for sarcoma prior to referral, of which eight had been re-excised. Twenty-four patients had not been staged prior to excision despite having a positive fine needle aspiration (FNA) in four cases. Eighteen patients (26%) had FNA or biopsy prior to imaging or referral.

Conclusion: Forty-six percent of sarcoma patients had not been treated according to the recommended guidelines. Forty-nine percent of these had inadequate primary sarcoma excision and this may have compromised their outcome. Orthopaedic surgeons had the best record for following the guidelines at 74% of referrals but this could be further improved. Doctors and especially surgeons need to be more aware of the principle of early referral of patients with suspected sarcomas.