A comparison of lateral release rates in fixed- versus mobile-bearing total knee arthroplasty.

BACKGROUND: With increasing functional demands of patients undergoing total knee arthroplasty, mobile-bearing (MB) implants were developed in an attempt to increase the functional outcome of such patients. In theory, with MB implants, the self-alignment should reduce the rate of lateral release of the patella, which is usually performed to optimise patellofemoral mechanics. This study reports on the lateral release rates for the P.F.C. Sigma® MB posterior-stabilised total knee replacement (TKR) implant compared with its fixed-bearing (FB) equivalent. MATERIALS AND METHODS: A total of 352 patients undergoing TKR were randomly allocated to receive either MB (176 knees) or FB (176 knees) posterior-stabilised TKR. Further sub-randomisation into patellar resurfacing or retention was performed for both designs. The need for lateral patellar release was assessed during surgery using a 'no thumb technique', and after releasing the tourniquet if indicated. RESULTS: The lateral release rate was the same for FB (10 %) and MB implants (10 %) (p = 0.9). However, patellar resurfacing resulted in lower lateral release rates when compared to patellar retention (6 vs 14 %; p = 0.0179) especially in MB implants (3 %). CONCLUSIONS: It has been previously reported that alterations to the design of the P.F.C. system with a more anatomical trochlea in the femoral component improved patellar tracking. The addition of a rotating platform tibial component to the P.F.C. Sigma system has, on its own, had no impact on the lateral release rate in this study. Optimising patellar geometry by patellar resurfacing appears more important than tibial-bearing design. Although MB implants appear to reduce the need for lateral release in the P.F.C. Sigma Rotating Platform, this only occurs when the patellar geometry has been optimised with patellar resurfacing. LEVEL OF EVIDENCE: Level 2.

A prospective randomised study comparing rotating platform and fixed bearing total knee arthroplasty in a cruciate substituting design--outcomes at two year follow-up.

BACKGROUND: Fixed bearing (FB) total knee replacement is a well established technique against which new techniques must be compared. Mobile bearing (MB) prostheses, in theory, reduce polyethylene wear but the literature is yet to provide evidence that they are superior in terms of function or long-term survivorship. In addition there has been no comparison of patella resurfacing on the outcome of either design. The aims of this randomised prospective study were firstly to determine whether a mobile bearing prosthesis produced better clinical outcome and range of motion at two year follow-up and secondly to assess the effect of patella resurfacing on the outcomes of both types of bearing design. METHODS: Three hundred fifty-two patients were randomised into receiving either a PFC Sigma© cruciate sacrificing total knee arthroplasty either with a mobile bearing or a fixed bearing, with a sub-randomisation to either patella resurfacing or patella retention. All patients participated with standard clinical outcome measures and had their range of motion measured both pre-operatively and at follow-up. RESULTS: The mobile bearing TKR design had no impact on range of motion; Oxford Knee Score and American Knee Society knee and function scores when compared to its fixed bearing equivalent. CONCLUSIONS: At two year follow-up there was no difference between the PFC Sigma© fixed and mobile bearing designs. With no clinical difference between the cohorts, we cannot recommend one design over the other. Long term benefits, particularly with regards to polyethylene wear, may yet be demonstrated. Level of evidence--1B.

The painless fracture: could it be TB?

Tuberculosis is one of the commonest infections world-wide, with one third of the world's population carrying the bacillus. Since the 1980s the decline in notification rates in the UK has stopped and recently reversed. The reasons for this are multifactorial and are discussed briefly here. We present the case of an unusual presentation of tuberculosis in the metatarsal of an elderly Caucasian gentleman. This serves as a reminder to include tuberculosis in the differential diagnoses of unusual musculoskeletal presentations.

Variation in applied force during insertion of cemented femoral prostheses.

Information is presented on forces applied to cemented prostheses during insertion. An instrumented femoral pusher was used to collect information during simulated operations on cadavers while using a laboratory test rig and during live surgery. Surgeons using flanged or collared prostheses tend to apply more force than those using collarless prostheses. There is a tendency for abrupt changes in applied force to occur when: 1) clearing cement; 2) easing hand discomfort; and 3) testing cement consistency. Tests showed that an overall impression of the force applied could be obtained from a laboratory simulation, but that clearing cement and testing cement were not modelled by this method. We discuss the implications of our observations in terms of prosthesis fixation and training of staff.

Mechanical symptoms arising from synovial pathology in knee joint.

Synovial pathology is a rare cause of mechanical symptom in the knee joint. The clinical features, arthroscopic appearance and histology of Hoffa's syndrome and localised villonodular synovitis are discussed.

Peak pressures in the forefoot.

We used a high frequency response, ultra-thin transducer to measure forefoot pressures at predetermined sites on the sole of the foot in 10 normal subjects. We demonstrated impact pressure peaks, which have not previously been identified, and which were separate from the roll-off peak. We report preliminary results on the effect of various forms of footwear and insoles on sub-pedal pressure during walking.

Biomechanical stability of four-part intertrochanteric fractures in cadaveric femurs fixed with a sliding screw-plate.

Three factors affecting the stability of four-part intertrochanteric fractures were considered; the type of reduction, the quality of bone as assessed by the Singh Index, and the position of the sliding screw within the head fragment. The stability of two different reductions of four-part intertrochanteric fractures created in paired cadaveric femurs was tested after fixation with sliding screw-plates. Cyclic loading over the range 1-6 times body weight was used to simulate physiological forces. The same loading regimen was applied to femurs with deliberately misplaced implants. Bone quality did not affect the incidence of failure. The type of reduction did not affect the incidence of failure, although it affected the mode of failure. Misplacing the implant greatly impaired the stability of the fracture. Thus, to minimize the risk of disruption of the reduced fracture every attempt must be made to ensure that the tip of the nail or plate lies between 5 and 12 mm from the subchondral bone of the femoral head and the shaft of the device in the central third of the neck on both anteroposterior and mediolateral radiographs.

Some factors affecting the strength of the cement-metal interface.

A manufacturing technique to increase the bonding between bone cement and metal prostheses has been assessed in the laboratory by "push-out" tests, and the effects of contamination of the cement and of the prosthesis with blood and intramedullary contents have been studied. The technique, known as pre-coating, increases bond strength; this increase is preserved after contamination of the cement which does, however, cause some lowering of interface shear strength. The implications for clinical practice are discussed.

Diagnostic arthroscopy of the knee in children.

Seventy-two symptomatic knees were studied in 68 patients between 2 and 17 years of age. A firm clinical diagnosis was made in all knees before arthroscopy. The clinical diagnosis and the arthroscopic findings were compared to establish the accuracy of the clinical diagnosis. This was 42% in children under 13 years old (Group 1) and 55% in children between 14 and 17 (Group 2). Possible unnecessary arthrotomy was avoided in 58% of the knees in Group 1, and 31% of the knees in Group 2. The most common "incorrect" clinical diagnosis in Group 1 was that of a discoid lateral meniscus followed by a torn medial or torn lateral meniscus in that order. The most common "incorrect" diagnosis in Group 2 was a torn medial meniscus followed by a discoid lateral meniscus. It is considered that children presenting with knee symptoms should be managed by orthopaedic surgeons who are experienced in arthroscopic diagnosis.

The Lenox Hill derotation brace in chronic post-traumatic instability of the knee.

Nine Lenox Hill derotation knee braces have been fitted for post-traumatic ligamentous instability of the knee. Eight of the patients found it an effective appliance for preventing their knees giving way, and wear it regularly. We would recommend this brace for cases of post-traumatic instability of the knee when the ligaments are at fault and provided that internal derangements such as meniscal tears or loose bodies have already been treated.

Therapeutic arthroscopy of the knee.

Sixty-six patients were reviewed after 70 therapeutic arthroscopy procedures. The procedures carried out included partial meniscectomy, removal of loose bodies, lateral release and synovial plica division. The commonest procedure performed was partial meniscectomy. The 32 patients undergoing arthroscopic meniscectomy were compared with a similar group of patients undergoing open meniscectomy as regards their duration of hospital stay, operation time and rehabilitation.

Carpometacarpal dislocation of the little finger.

A case is reported of dislocation of the base of the fifth metacarpal treated by manipulation and percutaneous fixation with a Kirschner wire. Visualisation by the image intensifier confirmed the reduction. A lateral view is important to control the volar displacement.

A report of 3 cases of simultaneous Colles' and scaphoid fractures.

Three cases of simultaneous Colles' and scaphoid fractures, one bilateral, occurring in a series of 422 Colles' fractures are presented. The factors necessary for the occurrence of such injuries are discussed.