Comparison of Clinical Results of the Third, Fourth, and Fifth Generations of the Hospital For Special Surgery Prosthetic Knee Implant

Presented at the Pennsylvania Orthopaedic Society - Fall 1999, Farmington, PA

Raymond P. Robinson, M.D., F.A.C.S., Virginia Mason Medical Center, Seattle, WA
Clinical Associate Professor, University of Washington, Seattle, WA

Purpose

This report outlines the design evolution of the Hospital for Special Surgery (HSS) series of knee implant designs and their progress over 28 years through five generations of the series. Throughout the history of this design, a systematic endeavor has been in progress that involved: a) defining the clinical problem of the arthritic knee, b) determining knee design objectives to solve identified problems, c) implant design, d) clinical evaluation, e) retrieval analysis, and f) implant redesign.To aid in the continuing evaluation of this lineage, a comparison of clinical results in the latest three generations was carried out using data compiled prospectively in the author’s practice.

History

The “first generation” HSS knee was the Duocondylar, designed by Drs. Peter Walker, Chitranjan Ranawat and John Insall. The first prosthesis of this series was implanted in December 1971. Clinical trials published in 1976 at two to four years follow-up reported five “disadvantages” with respect to the design:

(a) The implant did not replace the patellofemoral joint.

(b) Cement was not easily contained beneath the components.

(c) Fixed curvature of the femoral component made it difficult to insert properly in deformed knees.

(d) Preservation of the intercondylar tibial eminence with the posterior cruciate ligament interfered with the correction of deformities.

(e) Fixation of the separate tibial plateau components were not as secure as a large one-piece tibial component.

The addition of a patellofemoral replacement surface was eventually made to the Duocondylar, which then became known as the Duopatellar.

These clinically observed shortcomings led to the development of the “second generation” HSS knee, the Total Condylar. This design, first implanted in 1974, was also designed by the HSS Department of Biomechanics team of Walker, Ranawat and Insall. A 1979 report of the first 220 Total Condylar knees performed at HSS described 93 percent excellent and good results at three to five years. These results were a dramatic improvement over those of the Duocondylar/Duopatellar design.As a result, most of the fundamental design features of the Total Condylar implant, particularly the full radius medial/lateral geometry of the femoral and tibial condyles, became familiar features in the subsequent HSS knee designs.

The Insall/Burstein^® Posterior Stabilized Knee (IB) represents the “third generation” of HSS knees. First implanted in 1978, the IB was designed by a new HSS Team, headed by Drs. Albert Burstein and John Insall. Initial clinical results with the IB implant were reported in 1982. In 118 knees followed for two to four years, there were 96 percent excellent and good results using the HSS scoring system and a 94 percent rate of implant survival was reported at 13 years follow-up. However,a significant increase in patellofemoral complications was noted.

The “fourth generation” HSS knee was the Insall/Burstein^® Posterior Stabilized II (IB I),introduced in 1988. Clinical results of the IB II prosthesis have paralleled those of the original IB implant in terms of good and excellent results. Patellar fractures as described by Insall with the original IB design were reduced. However, significant patellofemoral pain problems and patellofemoral soft tissue entrapment persisted.

Continued clinical and retrieval observations and investigations led to the development of a “fifth generation” HSS knee in 1994. Design modifications were defined by the HSS Department of Biomechanics design team, lead by Dr. Burstein. The Exactech^® Optetrak^® Knee System is one such rendering of the concepts put forth by an HSS team and refined by an external surgeon-based design team. While historical core design concepts were retained, important changes in condylar geometry and anterior flange design were implemented to address articular stress and patellar performance.

Clinical Evaluation Materials and Methods

Since 1981, the author has used the HSS style posterior stabilized knee through three generations of its design (IB, IBII, Optetrak). Each time a new generation of the HSS knee design was introduced, a detailed prospective study was performed to assess the early clinical results.

All surgeries were performed or closely supervised by the author. Data was accumulated prospectively throughout all generations. All implants were posteriorly stabilized. Surgeries were carried out via midline exposure using “anterior femoral rough cut” style instruments. All components were cemented and the tibial component always utilized a trapezoidal central peg. Criteria for performing lateral release and popliteal release remained constant.

A total of 376 patients having 483 serially implanted knees comprised the entire study population (Figure 1). Each generation had at least 90 percent of patients having degenerative joint disease as the primary diagnosis. Average age of the patients in each generation was 69 years. Average weight was 78, 86, and 70 kilograms for IB, IB II, and Optetrak, respectively.

Results

Results are listed in order of the three generations (IB, IB II, Optetrak) respectively (“NA” indicates data was unavailable). Decreasing average surgical time for unilateral knees can be seen in Figure 2. Rates of soft tissue release are detailed in Figure 3.

Follow-up times were one year, two years, and one year, respectively. Average knee flexion was 114, 117, and 118 degrees. CPM use was 39%, 13%, and 0%. Manipulation rate was NA, 9 percent, and 2 percent. Patellofemoral complications are shown in Figure 4 and HSS ratings in Figure 5.

Conclusions

Changes and consistencies in successive generations of design were based on implant performance assessed by clinical observations and retrieval analysis, as well as advances in manufacturing technology. Long-term results of the basic Total Condylar design, the predecessor of the three generations in this study, have demonstrated excellent implant survival rates.^1,2,3 The Optetrak design aimed at coupling polyethylene stress reduction with better patellar performance. Early clinical results of the Optetrak knee implant demonstrated progressive improvements with this “fifth generation” system based on previous HSS designs.

Marked improvements were documented in patellofemoral function as measured by patellar femoral pain and crepitus and revision scoring. These new enhancements were accomplished by modifying features of the implant, while retaining the basic design concepts of previous generations of bicondylar implants with proven long-term survivorship.

Insall/Burstein^® is a registered trademark of the Hospital for Special Surgery, New York, NY.

References

1. Ranawat CS and Boachie-Adjei O. Survivorship analysis and results of total condylar knee arthroplasty. Clin Orthop 226:6-13, 1988.

2. Scuderi GR, Insall JN, Widnsor RE, Moran MC. Survivorship of cemented knee replacements. J Bone Joint Surg (Br) 71-B(5):798-803, 1989.

3. Vince KG, Insall JN, Kelly MA. The total condylar prosthesis:10 to 12 year results of a cemented knee replacement. J Bone Joint Surg (Br) 71-B(5): 793-797, 1989.