ORIGINAL ARTICLE Biomechanical Evaluation of a High Tibial Osteotomy with a Meniscal Transplant Geoffrey S. Van Thiel, M.D., M.B.A.,1 Rachel M. Frank, B.S.,1 Aman Gupta, M.S.,3 Neil Ghodadra, M.D.,1 Elizabeth F. Shewman, M.S.,3 Vincent M. Wang, Ph.D.,2 Bernard R. Bach, M.D.,1 Nihkil N. Verma, M.D.,4 Brian J. Cole, M.D., M.B.A.,1 and Matthew T. Provencher, M.D., MC, USN1 ABSTRACT This study determines the biomechanical advantage and the optimal configuration of a high tibial osteotomy (HTO) and meniscus transplantation performed concurrently. Six cadaver knees were placed in a spatial frame, and an HTO was completed. Loading points between a mechanical 6 degrees of varus and 8 degrees of valgus were loaded to 800 N for medial meniscal intact, meniscectomized, and transplanted states. Posterior slope was also increased by 3 degrees in these specimens. Contact data was recorded. Peak pressures significantly increased in the meniscectomized state in every degree of varus/valgus (p < 0.05). For both peak and total medial compartment pressures, there was a significant drop (p < 0.001) between neutral and 3 degrees of valgus. Lateral compartment pressures linearly increased from varus to valgus orientation. There was no significant change in the pressure profile of the knee with a 3-degree increase in posterior slope. This biomechanical study confirms the hypothesis that an HTO improves the peak pressures in the medial compartment at all degrees of varus/valgus alignment in the setting of meniscal trans- plantation. Furthermore, the largest decrease in medial pressures was between neutral and 3 degrees of valgus, suggesting that perhaps neutral aligned knees could benefit from an HTO. KEYWORDS: Meniscus, transplant, tibial, osteotomy, high Downloaded by: Rush University. Copyrighted material. Meniscectomy is commonly performed in con- result of this increased contact pressure were elo- temporary orthopedics. It effectively addresses an quently described by Fairbank2 and have been shown irreparable and painful symptomatic meniscal lesion. to accelerate significantly the progression to articular However, meniscal deficiency also significantly de- cartilage and subchondral damage.3 Thus, meniscal creases the tibial contact area and increases the tibial transplantation has experienced increased clinical ap- contact stresses. Paletta et al1 showed that a total plicability in recent years. It is an evolving technology lateral meniscectomy can increase tibial contact pres- that has shown clinical and physiologic efficacy in sure by 235% to 335%. The changes that occur as a various studies.4–20 1Division of Sports Medicine, Department of Orthopedics; 2Sports rush.edu). Research Laboratory, Rush University Medical Center; 3Department J Knee Surg 2011;24:45–54. Copyright # 2011 by Thieme of Biomechanics, University of Illinois, Chicago, Illinois; 4Department Medical Publishers, Inc., 333 Seventh Avenue, New York, NY of Orthopaedic Surgery, Naval Medical Center San Diego, San Diego, 10001, USA. Tel: +1 (212) 584-4662. California. Received: September 14, 2010. Accepted: November 21, 2010. Address for correspondence and reprint requests: Geoffrey S. Van Published online: March 25, 2011. Thiel, M.D., M.B.A., Division of Sports Medicine, Department of DOI: http://dx.doi.org/10.1055/s-0031-1275401. Orthopedics, Rush University Medical Center, 1611 W. Harrison ISSN 1538-8506. Street, 2nd Floor, Chicago, IL 60612 (e-mail: Geoffrey_vanthiel@ 45 46 THE JOURNAL OF KNEE SURGERY/VOLUME 24, NUMBER 1 2011 One aspect of meniscal transplantation that re- MATERIALS AND METHODS quires further clarification is the role for a concomitant high tibial osteotomy (HTO). It has been proposed that Specimens patients with uncorrected varus malalignment do not Six fresh-frozen cadaver knees were available for testing achieve optimal outcomes with cartilage restorative pro- where the mean donor age was 57 years (range, 52 to cedures,21,22 and a high tibial valgus osteotomy can 65 years). There were five male and one female donors. improve long-term results. Thus, an HTO performed Anteroposterior radiographs were taken to determine with a medial meniscus transplant has the potential to anatomic alignment and to rule out any significant both unload the compartment and potentially improve osseous pathology. The average pretesting anatomic the outcome of a transplant in a varus knee.23,24 Fur- alignment was 4 degrees of valgus (range, 2 to 7 degrees) thermore, isolated realignment procedures have been as measured by computer software (MagicWeb; Visage shown to be an effective treatment for unicompartmental Imaging Inc., San Diego, CA) from the radiographs. arthritis.25–28 Once alignment was determined, the knees were grossly As such, there is a limited amount of evidence dissected down to the joint capsule. The capsule, medial available that would directly or indirectly support collateral ligament, lateral ligament complex, anterior meniscal transplantation with a realignment proce- cruciate, and posterior cruciate ligaments were retained. dure, and there is no literature that addresses the The patella, quadriceps tendon, and patellar tendon were direct biomechanical influence of a transplanted me- removed to facilitate exposure. An anterior arthrotomy niscus in the setting of a medial opening wedge was used to access the joint. HTO. In addition, even in a well-performed HTO, posterior tibial slope may be altered, thus changing Sample Preparation the mechanical function of the knee and potentially The femur of the dissected knee was placed in a polyvinyl providing different meniscal transplant loading chloride (PVC) potting cylinder and secured with dental characteristics. The purpose of this study is to clarify acrylic (Lang Dental, Wheeling, IL). The tibia was then the biomechanical effects of a realignment procedure placed in a Taylor Spatial Frame (Smith & Nephew, in a meniscal transplant. It is hypothesized that there Memphis, TN) and secured with two Shanz pins in the will be a synergistic decrease in medial compartment anteroposterior (A-P) plane and two half pins inserted pressures with the combination of a meniscus trans- medial and lateral at 1 cm below the joint line. The plant and an HTO in a simulated varus-aligned distal aspect of the Taylor Spatial Frame was mounted to knee. the tibia with half pins (Fig. 1). Downloaded by: Rush University. Copyrighted material. Figure 1 Testing setup. Tibia in Taylor Spatial Frame with femur in MTS machine and Tekscan sensors placed submeniscally. Real-time pressure measurements were collected in the medial and lateral compartments. EVALUATION OF HIGH TIBIAL OSTEOTOMY WITH MENISCAL TRANSPLANT/VAN THIEL ET AL 47 An osteotomy was then completed using a Stryker conditioned by loading it 10 times at 800 N. The neutral (Mahwah, NJ) oscillating saw (blade 18 mm position was then tested by loading the knee to 800 N in wide  0.89 mm thick) and a 1-inch thin osteotome. full extension under the assumption that 60% of the The osteotomy was initiated at 2 cm below the joint line force should be transmitted through the medial com- on the medial side and exited through the lateral cortex partment and 40% located in the lateral compartment. at 1.5 cm below the joint line. The removal of two This is consistent with previously published values for struts on the Taylor Spatial Frame allowed adequate knee pressure distribution between the medial and lateral access to complete the osteotomy. compartments. Once the tibia and the femur were secured in the To facilitate comprehension of the following testing apparatus and the osteotomy had been com- protocol, a brief description of the Taylor Spatial Frame pleted, the knee was mounted on a materials testing construct is warranted. The frame consists of proximal system (MTS Insight 5; MTS, Eden Prairie, MN) with and distal rings that span the site of the osteotomy and the femur attached superiorly to the actuator, and the are connected by six adjustable struts. Each strut has a Taylor Spatial Frame was left free to rotate distally. The scale that defines a number value for each position. Once knee was placed in extension and Tekscan sensors (K- the initial position is locked in, the number value for all Scan model 4000; Tekscan, Boston, MA) were placed six struts are entered into a Web-based proprietary submeniscally in the medial and lateral compartments software program (www.spatialframe.com). Each de- (Fig. 1) via insertion through the anterior arthrotomy. sired sagittal plane correction is then input into the The sensors were secured with hemostat clips to the software, and the required values for each strut are posterior capsule to ensure no sensor translation between determined by the program. sequential trials. Tekscan sensors are thin, flexible elec- Initially, the neutral position (or 0 degrees of tronic pressure transducers specifically designed for the mechanical alignment) was locked into place by securing knee that allow the measurement of pressures from 0.1 to the Taylor Spatial Frame, and the value on each strut was 172 MPa with an accuracy of 0.1 MPa. They are 0.1 mm recorded. The knee was then loaded twice to 800 N in thick and comprise two measuring fields, each with an the ‘‘neutral’’ position at a rate of 10 N/s with the final area of 33  22 mm and a spatial resolution of 0.1 mm. load held for 5 seconds. This loading protocol was then repeated with the knee sequentially positioned according to the testing conditions listed below. Each position was Testing Conditions determined by entering the desired sagittal plane angu- The initial ‘‘neutral’’ position was found by allowing the lation into the Taylor Spatial Frame software and adjust- knee to attain its resting position, which was defined as ing the struts to the prescribed values. These conditions mechanical neutral alignment (correlating with 6 de- were repeated for an intact, deficient, and transplanted grees of anatomic valgus alignment).