Instability is reported to account for around 20% of early TKR revisions. The concept of restoring the “Envelope of Laxity” (EoL) mandates a balanced knee through a continuous arc of functional movement. We therefore hypothesised that a single radius (SR) design should confer this stability since it has been proposed that the SR promotes normal medial collateral ligament (MCL) function with isometric stability throughout the full arc of motion. Our aim was to characterise the EoL and stability offered by a SR cruciate retaining (CR)-TKR, which maintains a SR from 10–110° flexion. This was compared with that of the native knee throughout the arc of flexion in terms of anterior, varus/valgus and internal/ external laxity to assess whether a SR CR-TKR design can mimic normal knee joint kinematics and stability. Eight fresh frozen cadaveric lower limbs were physiologically loaded on a custom jig. The operating surgeon performed anterior drawer, varus/ valgus and internal/external rotation tests to determine ‘maximum’ displacements in 1) native knee and 2) single radius CR-TKR (Stryker Triathlon) at 0°, 30°, 60°, 90° and 110° flexion. Displacements were recorded using computer navigation. Significance was determined by linear modelling (p≤0.05). The key finding of this work was that the EoL offered by the SR CR-TKR was largely equivalent to that of the native knee from 0–110°. The EoL increased significantly with flexion angle for both native and replaced knees. Overall, after TKR anterior laxity was comparable with the native knee, whilst total varus-valgus and internal-external rotational laxities reduced by only 1°. However, separated varus and valgus laxities at 110° significantly increased after TKR as did anterior laxity at 30° flexion. In conclusion, the overall EoL offered by the SR CR-TKR is comparable to that of the native knee. In the absence of soft tissue deficiency, the implant appears to offer reliable and reproducible stability throughout the functional range of movement, with exception of anterior laxity at 30° and varus and valgus laxity when the knee approaches high flexion. These shortcomings should offer scope for future work.
The U-shaped sacral fracture is a fracture pattern poorly recognized, that is not included in the standard classification of sacral fractures. These fractures are significant as they represent spino-pelvic dissociation, have a high incidence of neurological complications and information regarding modern treatment options is sparse. A number of authors have reported isolated cases or small series of patients with this type of fracture, although none explicitly note the bilateral vertical element that makes them U-shaped and represents spino-pelvic dissociation. We present four patients with U-shaped sacral fractures. All patients were polytraumatised patients of whom three had jumped from a height in suicide attempts illustrating the high energy required to produce this fracture. Three patients had ilio-sacral screw fixation, supplemented in one with instrumentation from the lumbar spine to the iliac crest. The other had sacral laminectomy with bony stabilization by instrumentation from the lumbar spine to the iliac crest without ilio-sacral screw fixation. No complications were encountered as a result of fixation. The fixation devices used essentially represent the local expertise that is available. The ilio-sacral screw technique is minimally invasive and appears to provide satisfactory fixation in our limited experience. However as fracture deformity often involves rotation of the upper sacrum, the use of a single screw may not provide adequate support against the deforming forces or allow reduction of the fracture. Additional ilio-sacral screws will provide some rotational control of the sacral fragment if their safe insertion is possible, if not then the forces should probably be neutralized by an additional device from L5 to the pelvis. The role of sacral decompression is unclear but may be appropriate in the presence of neurological deficit and a severely compromised sacral canal. These are complex, rare injuries. We recommend their referral to a specialized pelvis/spinal unit for definitive management.
The use of a valgus brace can effectively relieve the symptoms of unicompartmental osteoarthritis of the knee. This study provides an objective measurement of function by analysis of gait symmetry. This was measured in 30 patients on four separate occasions: immediately before and after initial fitting and then again at three months with the brace on and off. All patients reported immediate symptomatic improvement with less pain on walking. After fitting the brace, symmetry indices of stance and the swing phase of gait showed a consistent and immediate improvement at 0 and 3 months, respectively, of 3.92% (p = 0.030) and 3.40% (p = 0.025) in the stance phase and 11.78% (p = 0.020) and 9.58% (p = 0.005) in the swing phase. This was confirmed by a significant improvement at three months in the mean Hospital for Special Surgery (HSS) knee score from 69.9 to 82.0 (p <
0.001). Thus, wearing a valgus brace gives a significant and immediate improvement in the function of patients with unicompartmental osteoarthritis of the knee, as measured by analysis of gait symmetry.
We reviewed histologically the incidence and pathogenesis of the deposition of calcium pyrophosphate dihydrate (CPPD) crystals in the pseudocapsule, femoral and acetabular membranes and periprosthetic tissue at revision of 789 cases of failed total hip replacement. In 13, periprosthetic tissues were found to have deposits of CPPD crystals in areas of cartilaginous metaplasia; four also showed evidence of localised deposition of amyloid. None of the patients had a history of chondrocalcinosis in the hip or other joints. Cartilaginous metaplasia and other changes in periprosthetic tissues may predispose to the deposition of CPPD and associated localised amyloid.