Hindlimb secondary ossification centres abnormalities in 12 Dobermann littermates with unilateral quadriceps contracture: CT- study

Introduction/Purpose: Quadriceps contracture is reported in dogs as a congenital anomaly or as a complication of parasitic infection or trauma. It is often followed by muscular atrophy, hindlimb joints degen- eration and hyperextension, femoral torsion, hip subluxation, and dis- use osteoporosis. In young dogs, it also induces bone hypoplasia, since ossification is likely to be modified by loading abnormalities. The aim of this study is to describe the features of hindlimb secondary ossification centres (SOCs) in a Dobermann Pinscher litter affected by unilateral quadriceps contracture. Methods: Twelve 57-day-old dead Dobermann Pinscher littermates with unilateral quadriceps contracture of unknown origin were eval- uated. Their hindlimbs were imaged with computed tomography. Pres- ence, shape, and volume of SOCs were evaluated. Volumes of the SOCs of the affected limbs were compared with those of the unaffected limbs. Results: The affected limb was shorter and hyperextended. The femoral head tended to be subluxated, the distal femur was extra- rotated, the stifle was back-turned; the patella was subluxated medi- ally and proximally. The femoral head was flattened and the femoral trochlea was hypoplasic. The tibial plateau was tilted caudodorsally cranioventrally. The calcaneal tuberosity was slightly misshaped. The femoral head (1.23 ± 0.11 cm3 vs. 0.89 ± 0.13 cm3 ), tibial plateau (2.16 ± 0.22 cm3 vs. 1.80 ± 0.24 cm3), distal tibial (1.63 ± 0.17 cm3 vs. 1.25 ± 0.13 cm3 ), metatarsal and phalanges SOCs of the II and III digit were smaller in the affected limb (II metatarsal: 0.28 ± 0.02 cm3 vs. 0.24 ± 0.02 cm3; III metatarsal: 0.45 ± 0.04 cm3 vs. 0.41 ± 0.03 cm3; II proxi- mal phalanx: 0.09 ± 0.01 cm3 vs. 0.07 ± 0.01 cm3 ; III proximal phalanx: 0.13 ± 0.02 cm3 vs. 0.11 ± 0.01 cm3 ; II middle phalanx: 0.28 ± 0.02 cm3 vs. 0.24 ± 0.02; III middle phalanx: 0.08 ± 0.01 cm3 vs. 0.07 ± 0.01 cm3 ; all P < 0.05). Discussion/Conclusion: Despite a normal timing in SOCs develop- ment, the affected limb exhibited several skeletal abnormalities. Femoral head flattening and hip subluxation were probably due to con- stant compression produced by rectus femuri contraction. The action of the tibial quadriceps insertion prevented normal growth of the prox- imal tibial epiphysis, resulting in reduction of tibial plateau volume and abnormal orientation. The persistent muscular contraction also induced extra-rotation of the distal femur (unable to develop distally), proximal subluxation of the patella and genu recurvatum. Lack of patel- lar sliding likely caused femoral trochlear hypoplasia. The abnormali- ties in the tibial distal epiphysis and hindpaw may be explained by lack of weight-bearing and hock hyperextension. This study describes for the first time the SOCs alterations induced by unilateral quadriceps contracture in a Dobermann litter, which should be carefully consid- ered when planning a therapy.