Aaron A. Hofmann

Subvastus (Southern) approach for primary total knee arthroplasty

The subvastus or Southern approach to the knee had been described as early as 1929 but is not found in standard modern orthopedic textbooks. This approach for primary total knee arthroplasty (TKA) preserves the integrity of the extensor mechanism and maintains the vascular supply to the patella. To appreciate the potential benefits of this approach, a complete understanding of the surgical anatomy is essential. The benefits of the subvastus approach make it a valuable technique for primary TKA.

High Tibial Osteotomy with a Calibrated Osteotomy Guide, Rigid Internal Fixation, and Early Motion. Long-Term Follow-up*

Background: We studied the results of sixty-four valgus-producing high tibial osteotomies performed with the use of a calibrated osteotomy cutting guide and rigid internal fixation, and followed by early motion, in fifty-six patients who had medial unicompartmental osteoarthritis and varus malalignment. Long-term studies have demonstrated that a high tibial osteotomy performed with staple fixation and followed by immobilization in a cast has an expected survival rate of approximately 85 percent at five years and 60 percent at ten years (in studies of ninety-five knees and 213 knees, respectively). To the best of our knowledge, there are no long-term reports on high tibial osteotomies performed with a calibrated osteotomy cutting guide and rigid internal fixation and followed by early motion. Methods: The indications for high tibial osteotomy were medial unicompartmental osteoarthritis and varus malalignment. A lateral closing-wedge osteotomy was performed. The patients were reexamined to obtain a knee score, to make lateral radiographs of both knees, and to make a full-length anteroposterior radiograph (showing the entire lower extremity, including the hip and ankle) of the involved knee with the patient standing. Results: Twenty-one knees were treated with a subsequent total knee arthroplasty at an average of sixty-five months after the high tibial osteotomy. The remaining forty-three knees had a good or excellent clinical result, with an average knee score of 94 points at an average of 8.5 years after the osteotomy. Survivorship analysis showed an expected rate of survival, with conversion to a total knee arthroplasty as the end point, of 85 percent at five years and 53 percent at ten years. No patient had patella baja postoperatively. There were six complications: four superficial wound infections, one superficial-vein thrombosis, and one delayed union (union occurred at five months). Conclusions: High tibial osteotomy has been criticized because of a high rate of complications, a loss of effectiveness with time, and the difficulty of conversion to a total knee arthroplasty secondary to patella baja. In our series, in which an osteotomy was performed with a calibrated osteotomy cutting guide and rigid internal fixation and was followed by early motion, the rate of complications was low and approximately two-thirds of the knees had a good or excellent clinical result at an average of 8.5 years. Conversion to a total knee arthroplasty was accomplished without difficulty in the patients who had this procedure. We highly recommend high tibial osteotomy with a calibrated osteotomy cutting guide, rigid internal fixation, and early motion for patients who wish to continue an active lifestyle.

Treatment of infected total knee arthroplasty using an articulating spacer.

Twenty-six patients with late infected total knee arthroplasties were treated by debridement and removal of components and all cement, preserving collateral ligaments. At time of debridement, an articulating spacer was fashioned to allow partial weightbearing and knee range of motion (ROM) during rehabilitation. This spacer was implanted using antibiotic-impregnated bone cement. For this purpose, 4.8 g of powdered tobramycin was mixed with each 40-g batch of Simplex cement. Cement was applied early to the components, but applied late to the femur, tibia, and patella to allow molding to the defects and bone without adherence to bone. Patients received tailored intravenous antibiotic therapy for 6 weeks in addition to this antibiotic-impregnated cement for treatment of a variety of gram positive and gram negative organisms. All patients had cemented revision total knee arthroplasty using antibiotic-impregnated cement with standard cementing techniques used. All patients but 1 had reimplantation; this patient died of unrelated causes before revision. Range of motion before revision was 10° to 95°. Followup averaged 30 months (range, 13–70 months). The average Modified Hospital for Special Surgery Knee Score after revision was 87 points (range, 53–100 points), with 92% good to excellent results. Range of motion after reimplantation was 5° to 106°. There have been no recurrences of infection. Use of an articulating spacer to treat infected total knee arthroplasty improves ultimate ROM and soft tissue health and significantly decreases the risk of reinfection.

Complications with hydroxyapatite particulate separation in total hip arthroplasty

This study reports on the results of the implant and tissue analysis of clinically retrieved hydroxyapatite (HA)-coated implants. Five of the patients with fixed HA-coated stems had been clinically diagnosed with osteolysis. The semiquantitative histologic grading in these patients showed HA, polyethylene, and metal particles were all present (Grade 3+) in the osteolytic regions of the periprosthetic tissue. Additionally, inflammatory cells (Grade 3+) were present in these regions. Back-scattered electron (BSE) and correlated elemental analysis showed HA particulate was present in the polyethylene inserts. The HA could be distinguished from bone chips in the polyethylene based on morphology and anatomic number gray level differences. This study was limited in that no clinical results of particular HA-coated implant series were reported. Careful follow-up care in patients with coated devices is recommended.

Treatment of infected total knee arthroplasty using an articulating spacer : 2- to 12-Year experience

Fifty consecutive patients with late infected total knee arthroplasties were treated by debridement and removal of all components and cement, preserving the collateral ligaments. At the time of debridement, an articulating spacer was made to allow partial weightbearing and range of motion of the knee during rehabilitation. This spacer was implanted using antibiotic-impregnated bone cement. For this purpose, 4.8 g powdered tobramycin was mixed with 40 g Simplex cement. Cement was applied early to the components, but applied late to the femur, tibia, and patella to allow molding to the defects and bone without adherence to bone. Patients had tailored intravenous antibiotic therapy for 6 weeks for treatment of various gram-positive and gram-negative organisms. All patients had cemented revision total knee arthroplasty using antibiotic-impregnated cement with standard cementing techniques. Range of motion before reimplantation was 6°-91°. Followup averaged 73 months (range, 24-150 months). The average modified Hospital for Special Surgery knee score after revision was 89 points (range, 70-100 points) with 90% good to excellent results, excluding the results of patients with reinfection. Range of motion after reimplantation was 4°-104°. Six patients had recurrences of infection, and one patient with a poor postoperative range of motion had a fusion. Use of an articulating spacer achieved soft tissue compliance, allowed for ease of operation, reduced postoperative pain, improved function, and eradicated infection equal to standards reported in the literature. Level of Evidence: Therapeutic study, Level IV (case series-no, or historical controls)

Computer navigation versus standard instrumentation for TKA : A single-surgeon experience

Component alignment errors in total knee arthroplasty greater than 3° can be associated with poorer outcomes. This retrospective study seeks to determine if computer navigation can improve accuracy of component alignment in comparable patient populations. The efficiency and safety of the navigated technique is also evaluated. Fifty total knee arthroplasties done using an imageless navigation system and 50 cases using standard instrumentation were compared. The same surgeon used a single system (Zimmer-Natural Knee™) in all cases. Long-standing radiographs collected at 6-week followup were measured for component orientation. When the navigation system was used 98% (49 of 50 cases) of all femoral components and 100% (50 of 50 cases) of all tibial components were placed within ± 3° of the radiographic goal position. There was a decrease in the standard instrumentation group to 90% (45 of 50 cases) and 92% (46 of 50 cases) within ± 3°, respectively. There was a difference in the standard deviations observed for the navigated cases and the conventional cases when femoral and tibial component position was considered. Average tourniquet time was 68 minutes in the navigated group and 57 minutes in the conventional group. There were no technique specific complications associated with the navigation system. This system affords the surgeon the potential to reduce outliers with regard to component position without an increase in complications. Tourniquet times were increased with the use of the computer. Level of Evidence: Therapeutic study, Level III-1 (retrospective comparative study). See the Guidelines for authors for a complete description of levels of evidence.

Implications of reference axes used for rotational alignment of the femoral component in primary and revision knee arthroplasty

A careful review of the literature revealed that no data had been reported on the angular difference or similarity between the posterior condylar axis used by many surgeons for primary total knee arthroplasty and the transepicondylar axis, which has been considered a useful anatomical landmark for femoral component placement in revision total knee arthroplasty. The purpose of this study was to determine whether measurable differences exist between the posterior condylar axis and the transepicondylar axis of the human femur. Nineteen pairs of human donor femora were measured. This study demonstrated that when the posterior condylar axis was taken as 0 degrees of rotation, the transepicondylar axis was found to be approximately 5 degrees externally rotated for both right and left femora, a significant difference (P < .05). However, there was no statistically significant difference in the angle measured between the posterior condylar axis and the transepicondylar axis when comparisons were made between matched right and left femora (P > .05). It is suggested that this information can be applied to improving the techniques currently used in the placement of both primary and revision femoral knee components.

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.

Ten- to 14-year clinical followup of the cementless Natural Knee system

Of 300 consecutive knees (238 patients) that had undergone arthroplasty with the cementless Natural Knee prosthesis from 1985 to 1989, 176 knees (141 patients) were available for followup at an average of 12 ± 1 years after the operation. Knee function was improved significantly. Modified Hospital for Special Surgery knee scores improved from 59.1 ± 13.2 points preoperatively to 97.8 ± 4.7 points at last followup. At last followup, knee range of motion averaged 0° ± 2° to 120° ± 10°. Implant survival was 93.4% (including infection and simple polyethylene exchanges) and 95.1% (excluding infection and simple polyethylene exchanges) at 10 years when applying the Kaplan-Meier survival analysis, using loose components, revision, or both as failure criteria. Besides the three revisions for infection, only two femoral and one tibial component required revision. The patellar component survivorship at 10 years was 95.1%. All patellar revisions were attributed to edge wear. Subsequent operative and design changes, including patellar component medialization and countersinking, have decreased the incidence of patellar revision. The long-term results of this cementless knee system compare favorably with those of cemented systems. The Natural Knee design has provided excellent and predictable long-term clinical results in the current series of active patients.

Cementless total knee arthroplasty in patients 50 years or younger.

Total knee arthroplasty now is being advocated for use in younger patients with posttraumatic and rheumatoid arthritis. Advances in technology, design, and materials potentially have allowed for more predictable results. There has been continued interest in cementless fixation for use in younger patients. Between 1986 and 1998, 75 total knee replacements in 57 patients 50 years or younger were done. All surgeries were done by one surgeon (AAH). There were 35 left knees and 40 right knees. The average age of the patients was 42 years (range, 31–50 years). Followup averaged 111 months. Preoperative range of motion was 5° to 106° and postoperative range of motion was 2° to 113°. Modified Hospital for Special Surgery knee scores improved from an average of 67 points preoperatively to an average of 97 points postoperatively. The majority of the diagnoses were posttraumatic arthritis or osteoarthritis (57%), indicating a young, active group of patients. There were two infections and 12 polyethylene exchanges. There were no revisions for loosening or implant failure. There was a correlation between prior knee surgeries and the need for a manipulation. Radiographically, there were no loose implants. Cementless fixation in the young patient with high physical demands was clinically reliable.