Purpose

Bone morphogenic protein (BMP-2) is used in spinal arthrodesis to induce bone growth. Studies have demonstrated that it achieves similar fusion rates compared to iliac crest bone graft when used in instrumented fusions. Our study aims at evaluating the requirement for instrumentation in one and two-level spinal arthrodeses when BMP-2 is used in conjunction with local bone to achieve fusion.

Purpose: The current gold standard for spinal arthrodesis, autologous bone graft harvested from the iliac crest, has several disadvantages including donor site morbidity, blood loss, delayed wound healing, and increased operative time. Our study explores a Demineralized Bone Matrix-Calcium Sulfate(DBM-CaSO4) composite graft with autologous bone marrow aspirate (BMA), and compares it to autologous iliac crest bone graft in lumbar and lumbosacral spinal fusions.

Method: A total of 80 patients were recruited for the study and randomised, via a computer-generated ran-domisation schedule, to autologous iliac crest bone graft (control) or DBM-CaSO4 composite graft with BMA (study) groups. Patients were evaluated at three-months, six-months, 12-months and 24-months post-operatively with questionnaires to evaluate clinical outcome (Oswestry disability questionnaire (ODI), visual analogue pain scales (VAS), and validated SF-36) and with posteroanterior and lateral x-rays of the spine to evaluate radiological outcome.

Results: At 24-months post-operatively, there were no statistical differences seen between the two groups based on the clinical outcomes measured. Average ODI values were 27.19 for the control group versus 22.68 for the study group (p > 0.05). The average back VAS pain for the control group was 3.50 versus 3.51 for the study group (p > 0.05). The SF-36 score was 89.22 for the control group versus 91.56 for the study group (p > 0.05). The average operative time was 115.7 minutes for the control group versus 104.2 minutes for the study group (p: 0.014). Average calculated blood loss was 571.9 cc for the control group versus 438.2 cc for the study group (p: 0.025). The Lenke score was 1.92 for the control group versus 2.66 for the study group (p: 0.004).

Conclusion: At two year follow-up, radiographic fusion was slightly higher in the ICBG. However, clinical outcomes were equivalent in both groups. Moreover, the DBM-CaSO4 and BMA composite graft offered the advantages of decreased blood loss and shorter operative time. Therefore, the DBM-CaSO4 and BMA composite graft represents a viable alternative to autologous iliac crest bone graft in carefully selected patients undergoing spinal arthrodesis.

Purpose: The purpose of this study was to report the mid-term survival results of Oxford UKAs in patients of 50 years of age or less, using (1) revision surgery and (2) Oxford Knee Scores (OKS) as outcome measures.

Method: A literature review identified studies of Oxford mobile bearing UKAs containing individuals 1) 50 years old or less with 2) medial osteoarthritis and 3) 2 years or longer follow-up. Authors were approached to participate in a multi-centre survival analysis by submitting all their patients, 50 years of age or less, who received a medial UKA for osteoarthritis. Patients who had died, been lost to follow-up or who underwent revision were identified. OKS were established for all patients with surviving implants.

Results: Seven centres submitted 107 patients. The mean age was 47 years (range 32–50). The average follow-up was 4 years (range 1–25). Forty-seven patients had follow-up into their fifth year or longer. The cumulative 7-year survival using revision as the endpoint was 96% (CI 8). The mean post-operative OKS for surviving implants was 38 (CI 2) out of a possible 48.

Conclusion: While early survival rates and function are encouraging, long-term follow-up is required before concluding UKA is a viable treatment option in young patients with unicompartmental knee arthritis.

Introduction: Restoration of predictable and normal knee kinematics after a TKR can improve the patient’s function. Traditional designs exhibit grossly abnormal kinematics with the femur subluxing posteriorly in extension and a paradoxical forward slide in flexion. In addition, the kinematics are very variable. Newer designs were intended to overcome these problems, owing to their ability to provide ‘guided motion’ of the components. The medial pivot knee uses a specifically designed articulating surface constraining the femoral component to externally rotate about an axis through the medial compartment.

This study assesses the functional in vivo kinematics of Advanced Medial Pivot (AMP) TKR and compares it to kinematics of the normal knee.

Methods: Thirteen patients with pre-operative diagnosis of primary osteoarthritis, who had undergone a knee replacement with the AMP knee at least one-year prior were recruited in this study. All had an excellent clinical outcome (as assessed by AKSS) and underwent fluoro-scopic analysis whilst performing a step up activity. Knee kinematics were assessed by analysing the movement of the femur relative to the tibia using the Patella Tendon Angle (PTA) through the range of knee flexion. This data was compared to that of thirteen normal knees.

Results: The PTA for the normal knee has a linear relationship with knee flexion. The PTA is 14 degrees in full extension and decreases to -10 degrees at 100 degrees knee flexion during a step-up exercise. Between extension and 60 degrees of knee flexion, no significant difference was found between the PTA for the normal knee and for the AMP. The PTA for AMP is significantly higher for values of knee flexion exceeding 60 degrees. The standard deviation for different values of knee flex-ion is similar to that seen in the normal knee.

Conclusions: In extension, the PTA is near normal but in flexion PTA is higher than normal suggesting that the femur is too anterior. The variability of the kinematics for AMP TKR is similar to that of the normal knee and is better than that of most other knee designs that we have studied in the past, indicating that it is a stable TKR.

The aim of total knee arthroplasty (TKA) is to align both the femoral and tibial components perpendicular to the mechanical axis of the leg. Most instrument systems cut the femur and tibia independently. Accurate alignment of the femoral component is hampered by our inability to define precisely the centre of the hip in three-dimensional space. Femoral resection is therefore based on a number of assumptions, which unfortunately do not hold true all of the time.

First, it assumes that an intramedullary rod follows a predictable path in the femur; secondly, that there is a fixed relationship between the rod and the mechanical axis of the leg, and thirdly that the shape of the distal femur is constant. Fourthly, even if the resection is correct, it assumes that the femoral component sits perfectly on cut surfaces. Further, there are inherent inaccuracies in the assessment of femoral component position, in that rotation of the limb with a 10° fixed-flexion deformity greatly affects apparent component position.

The exact entry point into the femur also influences alignment in that an intramedullary rod placed through an entry point 10 mm anterior to the intercondylar notch of the femur gives a mean valgus angle of 8°. When the tibia is cut perpendicular to its long axis in the coronal plane, assuming 3° of tibial varus, the femur needs to be cut with the corresponding degree of valgus, i.e., 5°. Even this argument is based on a small number of cadavers and does not take account of variations in the anatomy of the distal femur. In particular, a valgus bow can result in valgus malposition of the component. Extramedullary alignment carries the problem of using only a surface representation of the centre of the hip in a single plane, which becomes inaccurate as the femoral jig is rotated.

Malalignment of the tibial component increases the stress on the ultra-high molecular weight polyethylene insert, predisposing it to increased wear and subsidence. Studies comparing intramedullary and extramedullary guidance systems for cutting the proximal tibia have shown that 71% to 94% of prostheses inserted with an intramedullary guide, and 82% to 88% inserted with an extramedullary guide, are within 2° of being perpendicular to the long axis of the tibia.

To set a benchmark for comparison with computer assisted and robotic techniques currently being developed, we felt that it was important to assess the accuracy of placement of both the tibial base plate and femoral component in the coronal plane using current guidance systems.

We developed a series of radiographs allowing accurate independent assessment of femoral and tibial components. A long anteroposterior view of the distal femur with the patient prone was used to assess femoral placement. Coned views of the proximal and distal femur on the same plate were used to assess tibial placement. Correct rotational alignment of the radiograph was confirmed by the profile of the components.

Using this technique, we radiologically assessed the varus/valgus alignment of the tibial components of 350 TKAs. All the tibial components were implanted using an extramedullary guide with no posterior slope. We implanted 96.3% of components within 2° of the perpendicular to the longitudinal axis of the tibia. In order to validate our radiological assessment, a subgroup of 40 knees was re-assessed on CT scan. Analysis of this subgroup showed a close correlation between the results using the two different methods (mean difference 0.88°, SD 0.75).

We also assessed the position of the femoral component in 362 TKAs. A subgroup of 32 knees, 18 with perfect alignment and 14 with imperfect alignment, underwent CT scout scan of the femur from which the mechanical axis of the femur could be measured. Radiologically, 92% of all components were implanted within 3° of the target value and 83% were within 2° of target. There was close correlation between the CT and radiological measurements in the subgroup. Deviation from the mechanical axis was 1.16° (− 2.5° to +2°) in the perfectly aligned knees, validating both surgical technique and radiological assessment.

Although the findings for the femoral components compared favourably with other studies, there was still room for improvement. We set out to achieve this through direct measurement of the mechanical axis of the femur. In a series of 80 TKAs, patients were subjected to a preoperative CT scout scan of the femur. We took care to eliminate rotational error. The angle between the slope of the distal femur and the mechanical axis of the femur was calculated. During surgery the distal cutting block (Wright Medical Medial Pivot Arthroplasty System) was applied directly to the distal femur without use of an intramedullary alignment rod and the angle corrected so as to be perpendicular to the mechanical axis. A right-angled jig resting on the anterior femoral cortex was used to assess the flexion/extension of the cut. Patients were scanned again postoperatively.

In 76 knees (95%) the femoral component was within 2° of the mechanical axis. The remaining three were within 3°. We continue to evaluate the technique with the use of a new jig, which allows incremental 1°-correction of the distal femoral cut.

In conclusion, accurate cutting of the tibia during knee arthroplasty is possible with careful use of extra-medullary instrumentation. The use of a simple pre-operative CT scan eliminates the errors inherent in intramedullary femoral systems and takes into account the femoral anatomy of each individual patient.

Robotic-assisted surgery may offer the opportunity of accurate placement of components. It is, however, likely to be both time consuming and expensive. We should not yet abandon thoughts of improving the use of our current mechanical instruments. Robots have yet to prove their superiority.