34th Annual Scientific Meeting proceedings

Osteochondrosis of the lateral or medial femoral condyle is a common devolemetal disorder in young and adolescent dog. It is resulting from a focal disruption of normal enchondral ossification. This is leading to thickening and retention of cartilage in the subchondral bone.   Chondromalacia, fissuring of the carriage is finally resulting in the formation of a cartilaginous flap (dissecate). At least in humans a correlation between osteochondrosis of the knee joint and mechanical axis deviations to valgus or varus exists and is well documented. Empirically this is also true for many of the affected dog breeds with higher prevalence of stifle OCD. There seems to be a higher breed predisposition in German Shepherd dogs and some giant breads as Great Danes, in which the lesion occurs exclusively on the lateral condyles. His dogs usually have a valgus conformation of the knee in relation to the whole limb mechanical axis. Dogs with a breed related varus of the hind limbs (e.g. American Bull terrieres) seem to have medial condylar OCD lesion only. Due to this association, de-loading the affected compartment of the joint may have a positive impact on joint function and future osteoarthritis progression. With standard treatment (debridement of de subchondral bed and flap removal), we can usually see further deterioration and collapse of the affected join compartment, probably due to ongoing overload.

In human orthopedics, the indication for distal femoral and high tibial osteotomies is not limited to the alignment of the quadriceps mechanism when addressing patellar instability. A more common indication is re-distribution of the axial loading forces from the lateral to the medial compartment of the knee joint and vice versa. This load shifting osteotomy is indicated in cases of overload of the lateral or medial compartment due to whole-limb valgus or varus malalignment. This means that a valgisation osteotomy, either on femur or tibia, is performed in cases with medial compartment overload (genu varum) and a varisation of the knee is indicated in cases of lateral compartment overload (genu valgum).  A number of ex vivo studies in human orthopedics have shown a significant reduction in compressive forces on the affected side of the joint due to ipsilateral varisation or valgisation  of the femur or the tibia, respectively.  Current  literature provides  evidence of effectiveness  for load shifting osteotomies in the knee of human patients.

Relatively recently, the technique of distal tibial valgisation (Distal tibial osteotomy - DTO ) has been introduced for the treatment of osteochondrosis of the medial talus in dogs. An iatrogenic valgus deformity (5-8°valgisation) of the distal tibia is performed in this technique to shift the loads from medial to the lateral joint compartment.  A very mild or no postoperative progression of osteoarthritis was documented clinically. However, the technique was not published yet and objective data regarding the long term outcome are still missing. Based on these experiences, the author applied the load shifting principle named as balancing osteotomies in a number of cases of osteochondrosis of the lateral or medial condyle of the femur.

This can be done in very young patients (4.5-6months) progressively with  temporal hemiepipysiodesis. A small reconstruction plate with one screw on each end is applied for several weeks over the growth plate (GP). In cases of a values correction the GP is blocked from medial, in cases of varus from lateral. I may be applied on distal femur or proximal tibia or both and can be performed on both limbs simultaneously. To avoid a re-bound effect the plate is left until an overcorrection of 5 degrees is achieved. In this very young patients no local treatment needs to be preformed (debridement) as there is usually no detached dissecate (only a subchondral lesion). In all cases treated with hemilaminectomy (12 dogs) a complete healing of the subchondral defect was confirmed on CT after implant removal.

In dogs older 6 months an acute balancing osteotomy needs to be performed. This can be either a balancing distal femoral osteotomy (b-DFO), a proximal tibia osteotomy (b-PTO) or a medial closing or opening TPLO (b-TPLO).  In this cases it may be necessary to remove the partially detached dissecate. Even in severe cases and older dogs where mosaicoplasty or synthetic resurfacing is applied to the lesion, a balancing osteotomy is still indicated to protect the affected compartment from further overload and in cases of resurfacing implants to avoid kiss lesions.

Balancing DFO is usually performed as an opening wedge osteotomy without the use of a jig, from a lateral and a medial approach depending on the indication. A jig is not mandatory as the trans-cortex in OWO is not transected and torsion does not need to be addressed.  In most cases a dedicated DFO plate was used. The use of TPLO-jig was mandatory for b-PTO, here a variety of plates were used (TPLO plate, CBLO plate, T-Plate). The degree of desired valgisation depends on the patient's initial frontal plane femoral angulation. For example in dogs indicated for valgisation that are presented with high or excessive distal femoral varus, the correction is targeting aLDFA values ​​of 90-92 °. In cases where the aLDFA values ​​are already in the lower reference range (94-96°), we over-correct ​​to aLDFA values ​​around 87-90 °. B-DFO is preferred over b-PTO however if aLDFA is in the borderline or in the lower reference range (91-93°) valgisation is performed on the tibia.  In a varisation osteotomy the target is an aLDFA value between 98-100°. In cases where this is not possible due to the risk of patellar luxation to the opposite side, we perform the balancing correction on the proximal tibia (b-PTO). Balancing TPLO (closing /opening) can be performed with or without a jig.

Based on preliminary results in a relatively limited number of  patients, balancing osteotomy appears to be a promising primary or complementary method in the management of OCD of the knee joint and tarsus and in some cases of elbow OCD. Long term studies and application to a larger groups of patients are indicated to confirm the efficacy especially as a treatment modality for OCD. At least in very young dogs the results are extremely encouraging.