Unilateral Genu Recurvatum and Tarsal Joint Dysplasia in a Juvenile Cat

Abstract

Introduction

Genu recurvatum is characterized by the abnormal hyperextension of the stifle joint. Herein, we describe the diagnosis and surgical management of unilateral genu recurvatum and tarsal joint dysplasia in a juvenile cat.

Case Report

A 2-month-old intact female Devon Rex cross was brought to our clinic after its owner observed unilateral (left) hindlimb lameness. Orthopaedic and imaging evaluations revealed hip joint laxity, genu recurvatum, and luxation of the calcaneoquartal and talocalcaneocentral joints. The cat underwent combination surgery involving femoral segmental ostectomy, temporary partial tarsal immobilization with subtalar joint fixation, and temporary stifle and tarsal joint immobilization using an external skeletal fixator.

Results

All temporary implants were removed within 4 weeks after surgery, except for the plate used for partial tarsal immobilization, which was removed after 4 months due to implant failure. Despite persistent hip dysplasia and signs of stifle and tarsal joint osteoarthritis, the cat demonstrated improved gait with only mild lameness 1 month after surgery, with further functional improvement maintained for at least 29 months.

Clinical Significance

Surgical correction of genu recurvatum and tarsal joint luxation may provide long-term functional improvements in juvenile cats, indicating that early surgical intervention can be considered for the management of such complex deformities.

Keywords

cat - genu recurvatum - tarsal joint dysplasia - external fixator

Introduction

Genu recurvatum is a deformity characterized by the abnormal hyperextension of the stifle joint, beyond the normal physiological range. An extreme case of genu recurvatum was previously found to be non-reducible through manual manipulation.[1] Although well documented in humans and often referred to as congenital dislocation of the knee (CDK) or patella (CDP), genu recurvatum is rarely reported in small animals, and its pathophysiology remains unclear. CDK, which involves varying degrees of joint subluxation or dislocation, is rare in humans. To the best of our knowledge, no previous case of surgical treatment for non-reducible genu recurvatum in cats has been reported. Herein, we describe a novel surgical approach combining femoral segmental osteotomy, joint stabilization, and temporary immobilization to correct this complex deformity.

Case Presentation

Case Details and Diagnosis

A 2-month-old intact female Devon Rex cross cat was brought to our institution by its owners for the evaluation and treatment of disuse of the left unilateral hind limb after being brought home. A veterinary physician initially prescribed 2 weeks of physiotherapy, which did not result in any improvement. A subsequent orthopaedic examination revealed laxity of the left hip joint, non-reducible genu recurvatum at the stifle joint, and tarsal varus deformity and laxity, while a radiographic evaluation confirmed laxity in the left hip joint, genu recurvatum with grade 4 medial patellar luxation at the left stifle, and luxation of both the calcaneoquartal and talocalcaneocentral joints on the left pelvic limb ([Fig. 1A, B]). Computed tomography revealed a relatively small patella and tarsal bones noted as additional findings, although long bone alignment appeared normal with no detectable deformities. The cat was diagnosed with unilateral hip dysplasia, genu recurvatum, and tarsal joint dysplasia.

Fig. 1 Preoperative and immediate postoperative radiographs of the left hindlimb. (A, B) Preoperative views showing hip laxity, stifle hyperextension, patella alta, medial patellar luxation, and tarsal malalignment. (C, D) Immediate postoperative views demonstrating femoral segmental osteotomy fixation, temporary partial tarsal immobilization, temporary subtalar joint fixation, and temporary immobilization using an external skeletal fixator.

Surgical Planning

A single-session surgery was planned, consisting of femoral segmental osteotomy (FSO) to reduce tension in the quadriceps femoris and facilitate the repositioning of the patella into the trochlear groove, along with temporary immobilization using an extraskeletal fixator (ESF) of the stifle and tarsal joints to aid in soft tissue realignment. Temporary partial tarsal immobilization was also planned.

Anaesthesia for Surgery

The following anaesthetic protocol was utilized in this case: premedication was performed using butorphanol, followed by propofol administration for the induction of anaesthesia. After endotracheal intubation was achieved, general anaesthesia was maintained using isoflurane in 100% oxygen, while an epidural injection of a compounded lidocaine and bupivacaine solution was administered for analgesia. Cefazolin was administered 30 min before surgery and every 90 min intraoperatively as a prophylactic antibiotic therapy.

Surgery

A skin incision was made from the tibial tuberosity to the greater trochanter. The quadriceps femoris muscle was carefully examined intraoperatively, which revealed no obvious contractures or fibrotic tissue. The FSO was performed first, during which a 7.5 mm shortening was stabilized using a distal femoral osteotomy (DFO) plate (Mathemedix Oy, Espoo, Finland) with an intramedullary pin (IMEX Veterinary Inc., TX, USA). Temporary partial immobilization was performed with a titanium locking plate (Suwa Ltd., Yamanashi, Japan) using an extra-articular approach. Rotational instability of the subtalar joint was fixed using a positional screw (Suwa Ltd., Yamanashi, Japan). Following the placement of pins in the femur, tibia, and metatarsal bones, an ESF was assembled to stabilize the limb using polymethylmethacrylate to replace the connecting bar.

Postoperative Management

The owner was instructed to confine the cat in a limited space in which it would be able to stand and walk on all four limbs without difficulty but the height of the space would prevent the cat from standing up on just its pelvic limbs. The width of the confined area was limited to approximately five times the length of the cat's body, and this restriction was maintained for 4 weeks after surgery. No other specific rehabilitation protocol was prescribed.

Postoperative Assessment

Postoperative evaluations were conducted at regular intervals, including physical examinations and radiographic assessments at 2, 4, and 29 months. The cat's gait was subjectively assessed by the attending surgeon, and lameness was graded on a scale of 0 to 5.[2] Radiographs were reviewed to evaluate bone healing at the osteotomy site, implant stability, bony morphology of the femur and tibia, and the development of osteoarthritic changes.

Ethical Considerations

All procedures were conducted in accordance with accepted veterinary standards. Informed consent was obtained from the owner for all treatments, as well as the publication of the clinical data and images included in this report.

Overall Findings

Postoperative radiographs confirmed the intended fixation angles: the stifle and tarsal joints were maintained at 90 and 105 degrees in the mediolateral projection, respectively ([Fig. 1C, D]). The frontal plane view demonstrated satisfactory overall limb alignment. After 2 weeks of surgery, follow-up radiographs revealed cranial displacement of the tibia with respect to the femoral condyles and early callus formation at the site of the femoral osteotomy, and a reduction in hip luxation was observed in the frontal plane. Based on these findings, the intramedullary FSO pins, ESF hardware, subtalar fixation screws, and the proximal end of the temporary partial tarsal immobilization were removed.

Radiographs obtained 1 month after surgery confirmed adequate bone healing at the osteotomy site; therefore, the DFO plate and the remaining screws were removed. Although the owner declined surgical treatment for hip dysplasia, the cat demonstrated improved gait with only mild postoperative lameness (grade 1). At 3 months postoperatively, the cat demonstrated improved limb function. The maximum flexion and extension angles of the stifle joint were 13.5 and 145.4 degrees, respectively, in the normal limb and 29.6 and 134.3 degrees, respectively, in the affected limb. For the tarsal joint, the corresponding angles were 16.9 and 162.9 degrees in the normal limb and 54.0 and 152.4 degrees in the affected limb.

Radiographs obtained 4 months after surgery revealed a broken plate at the site of partial tarsal immobilization, as well as signs of distal femoral deformity and stifle osteoarthritis. The failed implant was removed without any complications.

At the final follow-up, 29 months after surgery, the cat showed a good range of motion in all left pelvic limb joints and functional limb alignment with resolution of postoperative lameness (grade 0).

Radiographic evaluation revealed bilateral hip osteoarthritis, femoral shortening with varus deformity, and tibial valgus ([Fig. 2]). On the normal limb, the femoral length measured 89.3 mm with an anatomical lateral distal femoral angle (aLDFA) of 93.3 degrees, whereas the affected limb had a femoral length of 59.5 mm and an aLDFA of 102.9 degrees. Preoperative and postoperative final recheck clinical images demonstrating limb posture and range of motion are presented in [Fig. 3].

Fig. 2 Radiographic follow-up at 29 months post-surgery. Frontal (A) and mediolateral (B) views demonstrate maintained joint alignment, femoral shortening with varus deformity, moderate osteoarthritic changes in the hip and stifle joints, and mild osteoarthritic changes in the tarsal joint.

Fig. 3 Preoperative and postoperative clinical photographs. (A) Preoperative clinical image demonstrating abnormal limb posture associated with unilateral genu recurvatum and tarsal joint dysplasia. (B, C) Postoperative clinical images obtained at the final follow-up demonstrating improved range of motion of the left hind limb during flexion and extension.

Discussion

Genu recurvatum, characterized by stifle hyperextension, may present with clinical signs similar to those associated with quadriceps femoris muscle contracture.[1] In non-functioning limbs affected by quadriceps femoris contracture, fibrous adhesions can develop between the quadriceps muscle and fracture callus, contributing to joint stiffness.[3] In the present case, however, no evidence of quadriceps femoris muscle contracture or fibrotic adhesions was found, following a thorough, albeit subjective, intraoperative evaluation. Stifle reducible hyperextension has previously been reported as the hyperextension was an iatrogenic consequence attributed to over-rotation of the proximal tibia during the surgical procedure.[4] In contrast, no proximal tibial deformity was identified in the present case. Therefore, the cat's condition was considered to be consistent with congenital genu recurvatum. Computed tomography revealed relatively small patella and small tarsal bones, whereas radiography revealed coxofemoral dysplasia. Although similar findings have been reported as concurrent abnormalities in juvenile dogs (aged 55–57 days) diagnosed with quadriceps femoris contracture,[5] long bone deformities were also present in those cases, which were not observed in the present case. This discrepancy in imaging findings may indicate differences in the underlying pathophysiological mechanisms of these conditions.

Recent reports on the surgical management of quadriceps femoris contractures have described the use of dynamic or static flexion devices[6] [7] and transarticular ESF of the stifle joint[8] to maintain the joint in a physiologically flexed position. ESF has also been reported to provide effective stabilization in cases of shearing injuries of the tarsal joint.[9] Based on these reports, we conclude that ESF contributes to both maintaining the stifle and tarsal joints in functional flexion and providing temporary stabilization in the presence of joint instability.

The femoral deformity identified postoperatively was considered to have resulted from plate fixation extending across the distal femoral growth plate. This complication could have been prevented if the osteotomy site had been performed more proximally, allowing the plate to be positioned farther from the physis. Therefore, proper selection of the osteotomy level is crucial in growing animals to minimize the risk of iatrogenic physeal injury and subsequent angular deformity.

Morphological changes in the tarsal bones have been reported in human patients undergoing coaptation treatment for congenital talipes equinovarus,[10] suggesting that therapeutic intervention for congenital limb deformities may influence bone development during early growth. Similar tarsal dysplasia was observed in the present case, and the combination of temporary partial tarsal immobilization and subtalar fixation resulted in favourable outcomes, including morphological remodelling of the tarsal bones and restoration of joint alignment, with only mild radiographic evidence of osteoarthritic changes. These findings indicate the potential benefits of early surgical intervention in promoting increased physiological tarsal joint development in juvenile patients with congenital deformities.

This report is limited by its single-case nature and reliance on subjective intraoperative evaluation of the cat's musculoskeletal structures. Although computed tomography was performed in these cases, objective morphometric or volumetric analyses of the musculoskeletal anatomy were not conducted. Incorporating such quantitative assessments can provide definitive insights into soft tissue and skeletal abnormalities. Therefore, further accumulation of similar cases and long-term follow-up studies are necessary to better characterize the pathogenesis and evaluate the treatment outcomes of congenital genu recurvatum and its associated deformities in feline patients.

Despite these limitations, this case demonstrates that surgical correction of genu recurvatum and tarsal joint dysplasia can lead to a favourable long-term functional outcome. Surgical intervention can be a viable option for managing a complex congenital limb deformity in a kitten, particularly when conservative treatment fails to achieve adequate improvement.

Contributors' Statement

T.K.: study conception and design, surgery, data collection and analysis, and manuscript drafting and revision; K.S.: data interpretation, figure preparation, and manuscript editing; Y.K.: surgical assistance, clinical data collection, and manuscript review. All authors reviewed and approved the final version of the manuscript.

Conflict of Interest

The authors declare that they have no conflict of interest.

Acknowledgements

The authors would like to thank the veterinary technicians Satoko Okubo, Mayu Takanami, Misaki Tanioka, and Maaya Matuo for their dedicated care of the animal during the course of this study, as well as the animal's owners for their cooperation and trust in allowing the treatment and follow-ups necessary for this report.

• References

• 1 Simpson DJ, Lewis DD. Textbook of Small Animal Surgery. 3rd ed.. Philadelphia: WB Saunders; 2003
• 2 Huntingford JL, Fossum T. Fundamentals of physical rehabilitation. In: Fossum T. ed. Small Animal Surgery. 4th ed.. Philadelphia: Elsevier; 2013: 105-124
• 3 Bardet JF, Hohn RB. Quadriceps contracture in dogs. J Am Vet Med Assoc 1983; 183 (06) 680-685
• 4 Rial García A, Craig A. Stifle hyperextension identified in a dog with an excessively negative tibial plateau angle and a grossly intact cranial cruciate ligament following inappropriate cranial closing wedge ostectomy. Vet Rec Case Rep 2022; 10: e12345
• 5 Andreis ME, Polito U, Modina SC. et al. Hind limb ossification centre hypoplasia and deformities induced by quadriceps contracture: radiographic and computed tomographic study in 13 Doberman Pinscher littermates. Res Vet Sci 2021; 135: 184-191
• 6 Wilkens BE, McDonald DE, Hulse DA. Utilization of a dynamic stifle flexion apparatus in preventing recurrence of quadriceps contracture: a clinical report. Vet Comp Orthop Traumatol 1993; 06: 219-223
• 7 Fossum TW. Small Animal Surgery. 2nd ed.. Merchant T, Barber R. eds. St. Louis: Mosby; 2002: 1164-1167
• 8 Moores AP, Sutton A. Management of quadriceps contracture in a dog using a static flexion apparatus and physiotherapy. J Small Anim Pract 2009; 50 (05) 251-254
• 9 Corr S. Intensive, extensive, expensive. Management of distal limb shearing injuries in cats. J Feline Med Surg 2009; 11 (09) 747-757
• 10 Hamel J, Hörterer H, Harrasser N. Radiological tarsal bone morphology in adolescent age of congenital clubfeet treated with the Ponseti method. BMC Musculoskelet Disord 2021; 22 (01) 332

Publication History

Received: 08 September 2025

Accepted: 08 January 2026

Article published online:
20 January 2026