Total Knee Arthroplasty for Secondary Osteoarthritis in Patients With Multiple Hereditary Exostoses: A Case Series

Introduction

Multiple hereditary exostoses (MHE), also known as hereditary multiple osteochondromas, is a rare autosomal dominant skeletal disorder caused by mutations in the EXT1 or EXT2 genes, which are essential for heparan sulfate biosynthesis and normal chondrocyte differentiation. The disease is characterized by multiple benign, cartilage-capped bony outgrowths – known as exostoses or osteochondromas – most commonly arising from the juxta-epiphyseal regions of long bones. The estimated incidence is approximately 1 in 50 000 individuals, with strong familial inheritance and high penetrance [1]. In addition to genetic characterization, the recent literature has emphasized the broad spectrum of clinical presentation – including deformities, vascular or neural compression, and rare malignant transformation – and emphasizes the importance of advanced imaging modalities for diagnosis and surveillance. Clinically, MHE often presents in childhood with palpable bony masses, limb-length discrepancies, joint stiffness, and angular deformities such as genu valgus or varus. The knee is often affected; case series frequently cite valgus deformity as a recurring presentation, with exostoses commonly found around the distal femur and proximal tibia. With skeletal maturity, osteochondromas typically cease to grow; however, residual deformities, chronic malalignment, and joint incongruity predispose patients to early-onset secondary osteoarthritis (OA), particularly in weight-bearing joints such as the knees and hips [2]. Despite this clinical course, total knee arthroplasty (TKA) in patients with MHE remains uncommon. The limited number of case reports is likely due to the technical complexity involved, which includes challenges such as distorted joint anatomy, ligamentous imbalance, retained or incompletely excised exostoses, and a history of multiple prior surgeries. Another major challenge in TKA for patients with MHE is achieving adequate soft tissue balance. In such situations, the selective use of more constrained implants may improve medial-lateral stability. In addition, the use of navigation-assisted TKA can be useful for accurate bone resection and limb alignment. Given these complex anatomical and biomechanical conditions, successful TKA in patients with MHE requires meticulous preoperative assessment and flexible intraoperative decision-making, including the selective use of more constrained implants and alternative alignment strategies when necessary. In this report, we describe 4 cases of MHE treated with TKA for advanced OA, focusing on intraoperative challenges related to deformity, ligament balancing, implant selection, and the selective use of navigation assistance.

Case Reports

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A 66-year-old woman with a history of MHE presented with advanced knee OA. Preoperative radiographs showed valgus deformity, and the range of motion (ROM) was −10° in extension and 100° in flexion. Imaging revealed multiple osteochondromas and medial joint space narrowing. TKA was performed using the measured resection technique. After inflating the air tourniquet to a pressure of 250 mmHg, the knees were exposed with the medial parapatellar approach. The anterior cruciate ligament was absent, and the posterior cruciate ligament was sacrificed. The osteotomy was performed perpendicular to the mechanical axis, according to the preoperatively planned resection level and angle. The Persona^® implant system (Zimmer Biomet, Warsaw, IN) was used. The use of a posterior stabilized (PS) insert was planned, but residual medial laxity was noted in full extension. To address this, further soft tissue balancing was performed, including release of the popliteus tendon, and a constrained PS (CPS) insert was utilized. The hip-knee-ankle (HKA) angle improved from 204° preoperatively to 184° postoperatively. At the 6-year follow-up, the patient showed no instability, with a ROM of −5° in extension to 120° in flexion.

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A 66-year-old man with a history of MHE and previous femoral fracture treated with internal fixation presented with advanced knee OA. Preoperative radiographs showed valgus deformity, and the ROM was −5° in extension and 95° in flexion. TKA was performed using the measured resection technique. The procedure up to this point – including tourniquet application (250 mmHg), medial parapatellar approach, and osteotomy perpendicular to the mechanical axis – was the same as in Case 1. Intraoperatively, the femoral canal was obstructed due to retained hardware, necessitating the use of portable navigation (iASSIST^®; Zimmer Biomet, Warsaw, IN) for accurate bone resections. Trial reduction revealed persistent lateral instability in both extension and flexion. Extensive lateral release, including the iliotibial band and lateral capsule, was performed. The Persona^® implant system was used. A CPS insert was ultimately chosen to achieve satisfactory medial-lateral stability across the full range of motion. The HKA angle improved from 191° preoperatively to 183° postoperatively. At the 1-year follow-up, the patient showed no instability, with a ROM of 0° in extension to 100° in flexion.

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A 72-year-old woman with a history of MHE, including osteochondroma resection during childhood, presented with medial compartment OA of the left knee. Preoperative radiographs showed varus deformity, and the ROM was −30° in extension and 80° in flexion. TKA was performed using the measured resection technique. The procedure up to this point – including tourniquet application (250 mmHg), medial parapatellar approach, and osteotomy perpendicular to the mechanical axis – was the same as in Cases 1 and 2. Soft tissue balance was achieved intraoperatively without extensive release. The Persona^® implant system was used. A PS insert was selected without need for constrained inserts. The HKA angle improved from 168° preoperatively to 180° postoperatively. At the 2-year follow-up, the patient showed no instability, with a ROM of −15° in extension to 110° in flexion.

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The same patient as Case 3 later underwent right TKA for medial compartment OA. Unlike the left knee (Case 3), the right side had no prior surgical history related to MHE. Preoperative radiographs showed varus deformity, and the ROM was −5° in extension and 95° in flexion. TKA was performed using the measured resection technique. The procedure up to this point—including tourniquet application (250 mmHg), medial parapatellar approach, and osteotomy perpendicular to the mechanical axis – was the same as in Cases 1, 2, and 3. The Persona^® implant system was used. Ligament balance was satisfactory, and a PS insert was used to achieve satisfactory medial-lateral stability throughout flexion and extension. The HKA angle improved from 163° preoperatively to 178° postoperatively. At the 2-year follow-up, the patient showed no instability, with a ROM of −5° in extension to 120° in flexion.

All patients began active knee motion exercises and standing at the bedside or walking with crutches or a walker under the supervision of a physical therapist on the first postoperative day. At the final follow-up, all patients were able to walk without assistance. The mean 2011 Knee Society objective score improved from 48 preoperatively to 94.5 at the final follow-up, and the mean 2011 Knee Society functional score improved from 36 to 54.5. The clinical characteristics and perioperative outcomes of the 4 cases are summarized in Table 1.

Discussion

TKA in patients with MHE remains a technically demanding procedure due to distorted joint anatomy, residual osteochondromas, and soft tissue imbalance [3]. Nevertheless, our case series demonstrates that with meticulous preoperative planning, appropriate implant selection, and the use of intraoperative techniques – such as constrained inserts and navigation systems when indicated – favorable short-term clinical outcomes can be reliably achieved. Challenges encountered in these cases included valgus deformity exceeding 20°, blocked femoral canals due to retained hardware, and persistent instability even after standard balancing techniques. In such scenarios, constrained prostheses such as CPS inserts, which are designed to enhance medial-lateral stability, were useful for addressing persistent ligament insufficiency. However, increased constraint can theoretically result in higher stresses at the bone–implant interface, raising concerns regarding aseptic loosening or implant-related complications. Despite these concerns, recent clinical studies of constrained condylar designs, which include CPS implants, have demonstrated satisfactory mid- to long-term clinical outcomes and implant survivorship in complex primary TKA [4]. Accordingly, CPS inserts may be a reasonable option when selectively used to address residual instability, rather than as a routine choice in primary TKA. In addition to soft tissue instability, achieving accurate bone resection and limb alignment represents another major challenge in TKA for patients with MHE, particularly in the presence of retained hardware or distorted femoral canals. Navigation-assisted TKA has been reported as a useful adjunct in such cases. Computer navigation can increase precision of bone cuts and improve the assessment of limb alignment in both primary TKA and cases involving complex deformity [5]. In our series, navigation systems were particularly helpful in cases with obstructed femoral canals, allowing accurate alignment without the need for additional invasive procedures such as corrective osteotomy.

Similar challenges were reported by Kim et al [6] in their case series involving 5 knees in patients with MHE who underwent TKA. They emphasized the importance of meticulous preoperative planning and the judicious use of constrained implants. According to their report, constrained prostheses were used in 4 of the 5 knees, and femoral osteotomy was required in 3 cases to achieve appropriate limb alignment due to complex deformities. Likewise, Grzelecki et al [7] described a case of TKA combined with tibial osteotomy to address severe angular deformity. These reports show that in cases with severe deformity, bony realignment procedures may be necessary adjuncts to achieve optimal component positioning and overall alignment. In contrast to these reports, none of our patients required corrective osteotomy; despite this, short-term outcomes were favorable, with improvements in alignment, range of motion, and 2011 Knee Society scores. These findings suggest that careful preoperative planning and selective use of constrained inserts or navigation assistance can help avoid osteotomy in selected cases.

This study has several limitations. First, the number of patients was very small, which precludes any statistical analysis and limits the generalizability of our observations. Second, the follow-up period was short and only early postoperative outcomes were available. Although the mean 2011 Knee Society objective and functional scores improved postoperatively, long-term implant survivorship and patient-reported outcome measures (such as WOMAC or OKS) were not assessed. Furthermore, as this was a single-center series, the results may be influenced by selection bias and surgical expertise, reducing external validity. Finally, the lack of detailed genetic or family history data prevents us from correlating clinical presentation and surgical challenges with the underlying genetic background of MHE. These limitations, however, are partly inevitable given the rarity of this disorder.

Conclusions

TKA can provide reliable pain relief and functional improvement in patients with secondary OA due to MHE. Although distorted anatomy and soft tissue imbalance make the procedure technically demanding, favorable outcomes can be achieved through appropriate intraoperative decision-making. The selective use of constrained prostheses and navigation systems can be valuable options in cases with severe deformity. Further studies are needed to evaluate the long-term implant survivorship and functional outcomes of TKA in patients with MHE.