Ronald W. B. Wyatt

Effect of the Tibial Cut on Subsidence Following Total Knee Arthroplasty

In 33 total knee arthroplasties (TKAs) using instrumentation designed to cut the tibia with 0 degree posterior slope, ten tibial components demonstrated at least 2 mm of tibial component subsidence. These subsided components were implanted onto tibiae with an average of 8 degrees +/- 2 degrees difference between the preoperative, anatomic posterior slope and their postoperative posterior slope. The remaining 23 components, without subsidence, were implanted onto tibiae cut within 2 degrees +/- 2 degrees of their anatomic slope. To help understand these clinical observations, a laboratory study was performed to compare the load carrying capacity and the stiffness of tibial subchondral bone following two types of tibial cuts: one made perpendicular to the long axis of the tibia and the other made parallel to the articular surface of the tibia. Mock tibial baseplates mounted on paired cadaver tibiae were loaded in compression and force displacement curves were recorded. Tibiae cut parallel to the surface exhibited 40% greater load carrying capacity and 70% greater stiffness than the paired tibiae cut perpendicular to the long axis. The biomechanical data of this study indicated that cutting the tibia perpendicular to the long axis results in weaker bone that may be inadequate to support a tibial component. This may explain the higher incidence of clinical subsidence if the tibial cut is not made approximately parallel to the anatomic slope.

Bone scans after total knee arthroplasty in asymptomatic patients : cemented versus cementless

The natural history of bone scans after total knee arthroplasty (TKA) was studied in 26 patients with 28 cemented TKAs and 29 patients with 31 cementless TKAs. The bone scans were examined at specified postoperative intervals. Radionuclide activity of the femoral, tibial, and patellar regions was measured. Six patients who developed pain postoperatively were excluded. Bone scans immediately postoperative and at three months demonstrated increased uptake, which gradually decreased to baseline levels at ten to 12 months. Radioisotope uptake was comparable in the cemented and cementless groups, but was highly variable in individual patients and in each of the follow-up periods. A single postoperative bone scan cannot differentiate component loosening from early bone remodeling. Sequential bone scans, as a supplement to the clinical examination and conventional radiography, may prove useful in the diagnosis of TKA failure.

High tibial osteotomy. Use of an osteotomy jig, rigid fixation, and early motion versus conventional surgical technique and cast immobilization.

High tibial osteotomy (HTO) using conventional surgical technique and cast immobilization was compared to HTO using an osteotomy jig, rigid internal fixation, and early motion. Fifteen patients (19 knees) had conventional HTO. The mean preoperative femoral-tibial angle was 2.5 degrees of varus, and the mean postoperative angle was 6.5 degrees of valgus. Two knees were undercorrected and eight knees (42%) had associated complications. Twenty patients (21 knees) had HTO utilizing the new surgical technique and postoperative management. The mean preoperative femoral-tibial angle was 2.3 degrees varus, and the mean postoperative angle was 7.6 degrees valgus. One knee was undercorrected (less than 4 degrees valgus) and one knee (5%) had an intraoperative intraarticular fracture. High tibial osteotomy with an osteotomy jig to provide accurate correction, and rigid internal fixation to allow early motion, is an attractive alternative to conventional HTO.

Prophylaxis with Cefamandole Nafate in Elective Orthopedic Surgery

A prospective, randomized, double-blind study was conducted to determine the efficacy of cefamandole nafate in reducing infections in general orthopedic procedures. Of 743 patients initially entered into the study, 715 (362 on cefamandole, 353 on placebo) fulfilled the requirements of the protocol. The infection rate was 1.6% for the cefamandole-treated group and 4.2% for the placebo group. In operations lasting longer than two hours, there were two infections in the cefamandole group and seven infections in the placebo group (p less than 0.05). Staphylococcus aureus and gram-negative bacilli were the common pathogens. Adverse side effects were limited to transient elevations in liver enzymes.

Knee stability in orthotic knee braces

The ability of six commercially available orthotic knee braces to stabilize ligamentous injuries of the knee was evaluated using fresh cadaver specimens. Anterior, valgus, and rotational forces were applied to the intact knee, after the anterior cruciate and medial collateral ligaments were cut, and after application of the knee braces. Bony displacement was measured using half pins and an external fixator applied to the tibia and femur. There was a significant difference in brace per formance, most likely due to differences in brace de sign. Of the six braces tested, the 3D 3-Way Brace provided the greatest knee stability.

Total knee arthroplasty. Two- to four-year experience using an asymmetric tibial tray and a deep trochlear-grooved femoral component.

The design features of an implant system can be crucial to the success of cementless total knee arthroplasty (TKA). The implant system described in this study incorporates anatomic features including an asymmetric tibial tray that is smaller laterally than medially, and a deep trochlear-grooved femoral component. Two hundred consecutive primary total knees were implanted between October 18, 1985 and January 19, 1988 and were followed prospectively. One hundred ninety-two were implanted without cement. Clinical evaluation demonstrates good or excellent results in 96%, including a mean range of motion of 122 at two to four years after arthroplasty. Routine fluoroscopic spot roentgenograms have shown no complete radiolucency in this series of patients. Bone ingrowth was predictable if morselized autograft bone was interposed between implant and host bone. Implant retrievals demonstrated uniform bone ingrowth into the porous coating, increasing to 40% of the pore volume in the tibial tray at 27 months. Restoration of the normal kinematics appears to minimize the bone-implant stress permitting bone ingrowth fixation. The results of primary cementless TKA in this series is comparable to cemented TKA with the advantage of conserving bone stock.

Endosteal Bone Loss After Total Hip Arthroplasty

Femoral endosteal bone loss has been shown to be part of the natural aging process and may be a factor in femoral component loosening following total hip arthroplasty (THA). In this study, changes in the femoral medullary canal width in 30 patients with aseptic femoral loosening following primary THA were compared with 30 matched control patients. The rate of canal expansion on the operated side was twice that of the nonoperated side and four times that of the control. After the onset of symptoms in the failure group, the rate of femoral expansion of the operated side doubled. Iliac crest biopsies showed a decrease in male patients for osteoid surface and appositional and bone formation rates when compared with literature controls. These results suggest that femoral medullary canal expansion may be a factor in femoral component loosening following THA. The increased rate of canal expansion after the onset of symptoms demonstrates the need for early surgical intervention to avoid excessive bone loss.

Cementless total knee arthroplasty in patients over 65 years old.

Many factors influence the decision to implant a knee prosthesis with or without cement. Implant retrieval studies have demonstrated that bone ingrowth into porous-coated devices is possible even in older age groups. Early clinical follow-up observations suggest that cementless total knee arthroplasty can be successful in patients over 65 years of age, and need not be reserved for younger patients.

Experience with acetabular fractures.

Acetabular fractures, although relatively rare, are often serious injuries requiring complex treatment. Major associated injuries are common and the mortality rate continues to approach 20% (8). We retrospectively evaluated 38 acetabular fractures. Twenty-six fractures were treated operatively, with adequate followup available for 23. Anatomic reduction or reduction to within 3 mm was achieved operatively in 21 (81%). The average Harris hip score was 90. The five poorly reduced fractures had an average Harris hip score of 54. Twelve patients were treated nonoperatively with adequate followup available for nine. Six patients with nondisplaced or minimally displaced fracture treated nonoperatively had an average hip score of 96. Six patients had displaced fractures which failed to reduce with nonoperative treatment. Their average hip score was 59. This study reaffirms the importance of adequate fracture reduction in the treatment of acetabular injuries.

Combined Coventry-Maquet procedure for two-compartment degenerative arthritis.

The combined Coventry-Maquet procedure has been proposed as a means of treating dual-compartment degenerative arthritis of the knee. The procedure was investigated in a prospective study of 14 patients treated by combined high tibial osteotomy and tibial tubercle elevation. Preoperative scores averaged 50 points and scores at follow-up evaluation averaged 57 points with a modified 100-point total knee grading system. There were no excellent results, one good result, and 13 poor results. Five patients whose results were poor have since had total knee arthroplasty. The combined Coventry-Maquet procedure required too much dissection, had too high a complication rate, and yielded a minimal improvement in knee function and pain. Two-compartment degenerative arthritis should be treated by an alternative method, such as total knee arthroplasty, when surgical intervention is indicated.