Two cases of meniscal injury in the horse
Horse 1 is a 5-year-old Hanoverian mare who presented to the Veterinary Teaching Hospital of North Carolina State University for investigation of acute onset of severe right hind limb lameness of two days’ duration.
Upon physical examination severe distension of the right femoropatellar and medial femorotibial joint was observed.
Lameness was seen at the walk characterized by a shortened cranial phase to the right hind stride. Passive movement of the right hind limb including flexion of the upper limb was resented.
Standard radiographic views obtained of the right stifle did not show any abnormal findings.
Ultrasonographic examination of the right stifle showed focal hypoechogenicities and an abnormal shape of the meniscus cranial to the medial collateral ligament consistent with a medial meniscal tear (Figure 1a/b). In addition a focal fluid filled swelling over the abaxial surface of the medial meniscus was identified (View Video 1).
Figure 1a/1b: Vertical ultrasonographic image of the medial meniscus illustrating its abnormal position and shape of the meniscus as well as a large, irregular area of hypoechogenicity within. A frequently observed artefact creating a linear anechogenicity within the meniscus should not be mistaken for a lesion (Figure 1b).
Figure 1b:
Further diagnostic work-up/Treatment:
Prior to arthroscopic exploration of the medial and lateral femorotibial joints, a bone marrow aspirate was obtained from the sternal vertebrae for isolation and augmentation of mesenchymal stem cells and later injection of the medial femorotibial joint. During arthroscopic examination of the femorotibial joints using a cranial arthroscopic portal, a grade III medial meniscal tear (Walmsley et al. 2003) was identified. The tear was described as a complete vertical tear involving the cranial ligament and axial portion of the cranial horn and body of the medial meniscus (View Video 2; Figure 2a/b). The torn axial portion of the medial meniscus was released from its cranial attachment (Figure 3) and resected at its most caudal accessible point (Figure 4). All loose fibrous tissue was debrided using a motorized synovial resector. The caudal pouch of the medial femorotibial joint was inspected and no abnormal findings were recorded (Figure 5).
The horse was released from the hospital three days following arthroscopic surgery. Four weeks post surgery the medial femorotibial joint was injected with approximately 10 million bone marrow derived mesenchymal stem cells suspended in 2 ml bone marrow supernatant. It was recommended to box rest the horse for 2 months’ followed by a gradual increase of in hand walking exercise for a maximum duration of 40 minutes at 4 months post surgery. At this point a re-examination should determine the horse’s further management.
Figure 2a: Probe inserted into the vertical tear of the axial portion of the medial meniscus (MCF=medial condyle of the femur, MM=medial meniscus)
Figure 2b: Probe inserted into the vertical tear of the axial portion of the medial meniscus. The tear is full thickness and extends caudally underneath the MCF. (MCF=medial condyle of the femur, MM=medial meniscus)
Medial femorotibial joint arthroscopy illustrating the meniscal tear
Figure 3: The cranial ligament of the torn portion of the meniscus has been transected and the affected portion of the meniscus retroflexed. (MCF=medial condyle of the femur, MM=medial meniscus)
Figure 4: Visualisation along the vertical plane of the tear. The caudal limit can not be appreciated. (MCF=medial condyle of the femur, MM=medial meniscus)
Figure 5: Caudomedial portion of the medial meniscus. No lesions can be appreciated.
Horse 2, a 15-year-old Quarter horse barrel racing gelding was presented for investigation of chronic left hind limb lameness of insidious onset with sudden exacerbation approximately one month previously. The owner reported that the horse had received repeated intra-articular corticosteroid injections of the “stifle” on a yearly basis to maintain his exercise level.
Upon examination the gelding showed moderate femoropatellar and medial femorotibial joint effusion. At the trot in a straight line and on hard surface the horse was graded 4/5 lame in the left hind limb. It was impossible to complete hind limb flexion tests as the animal showed “shivers-like” behaviour.
Radiographic examination of the left stifle revealed new bone formation along the cranial margin of the intercondylar eminence of the tibia and focal subchondral radiolucencies at the distal extent of the lateral trochlear ridge of the femur at its junction with the lateral femoral condyle (Figure 6).
Figure 6: Flexed lateromedial radiograph of the left stifle. At the junction between the lateral trochlear ridge and the lateral condyle of the femur 3 focal subchondral radiolucencies can be appreciated (*). (>) New bone formation along the cranial margin of the intercondylar eminence of the tibia.
Ultrasonographic examination was suggestive of a horizontal tear and partial prolaps of the lateral meniscus when compared with the ultrasonographic appearance of the right lateral meniscus (Figure 7 and 8).
Figure 7: Vertical ultrasonogaphic image of the lateral meniscus showing hypoechogenic areas and prolaps of the meniscus. (Left = proximal)
Figure 8: The right lateral meniscus for comparison.
Diagnosis:
Left lateral meniscal tear, enthesiopathy of the cranial cruciate ligament and/or cranial meniscal ligament, focal subchondral bone lysis distal aspect left lateral trochlear ridge/cranioproximal aspect of left lateral femoral condyle.
Treatment:
Using a cranial approach, arthroscopy of the left lateral and medial femorotibial joint was performed. The septum between the medial and lateral femorotibial joint was found to be torn and upon visualisation of the lateral meniscus the visible portion of the meniscus and its cranial ligament was severely disrupted (Figure 9). Upon debridement of the area using a motorized synovial resector it became apparent that a horizontal tear was present in the cranial horn of the lateral meniscus (Figure 10, Video 3). The cranial meniscal ligament was partially intact. In addition to the horizontal tear involving the entire cranial aspect of the lateral meniscus a smaller, axial vertical tear of the lateral meniscus was identified which extended caudally underneath the lateral condyle of the femur (Video 4).
Probing of the area axial to the medial intercondylar eminence of the tibia located the radiographically visible new bone formation along the lateral border of the cranial cruciate ligament (Figure 11, View Video 5). The cranial cruciate ligament appeared thin and atrophied and a mass of ’bunched’, firm connective tissue was identified at the insertion site of the cranial cruciate ligament cranial to the medial intercondylar eminence of the tibia (Figure 12, View Video 6).
The articular cartilage of the lateral femoral condyle appeared irregular (cobblestone appearance) and showed areas of partial and full thickness cartilage erosion. The area of focal subchondral bone lysis at the junction between the distal lateral trochlear ridge and the lateral condyle was characterized by localized loss of cartilage but probing did not reveal access to any subchondral bone defects (Figure 13).
Arthroscopic exploration of the medial femorotibial joint and examination of the medial meniscus revealed very mild fraying of the free edge of the cranial meniscal ligament (Figure 14).
Figure 9: Upon visualisation of the lateral femorotibial joint fraying and fibre disruption of the lateral meniscus is seen. The lateral femoral condyle (LCF) shows areas of partial thickness cartilage loss.
Figure 10: Following debridement of loose meniscal tissue it can be appreciated that a portion of the lateral meniscus is missing subsequent to a horizontal tear.
Lateral femorotibial joint arthroscopy illustrating the meniscal tear
Axial vertical tear of the lateral meniscus
Figure 11: New bone formation (X) axial to the medial intercondylar eminence of the tibia (MICET) which is associated with the medial border of the cranial cruciate ligament.
Video 5: New bone formation axial to the medial intercondylar eminence of the tibia
Figure 12: A mass of ‘bunched’ torn fibres (X) at the insertion site of the cranial cruciate ligament consistent with chronic partial tearing of the ligament.
Video 6: Arthroscopic video illustrating the mass of torn fibres
Figure 13: The mark (<) indicates the area where radiographic evidence of focal subchondral bone lysis was observed.
Figure 14: Mild fraying of the free edge of the cranial ligament of the medial meniscus(X).
Postoperative management of Horse 2 consisted of strict stall rest for two months, followed by minimal in-hand walking exercise and stall rest for an additional 2 months prior to re-assessment.
References:
Walmsley, J.P., Phillips, T.J. and Townsend, H.G.G. (2003) Meniscal tears in horses: an evaluation of clinical signs and arthroscopic treatment of 80 cases. Equine vet. J. 35, 402-405.
Schramme, M.C., Smith, R.K., Jones, R.M. and Dyson, S. J. (2006) Comparison of radiographic, ultrasonographic and arthroscopic findings in 29 horses with meniscal injury. Proceedings 16th Annual Veterinary Symposium ACVS, 16, E24.
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