V-Vas: A New Concept in Unloader Knee Orthosis Design

The use of custom or off-the-shelf unloader knee orthoses in both single and double upright design configurations have been successfully used in the management of patients with medial compartment osteoarthritis of the knee (1-5). The mechanism to achieve this is a three point pressure system which creates an offloading moment of the affected compartment. How this offloading moment is achieved, is through a fixed or an adjustable structural frame being used as a counterforce to an adjustable strap(s) and/or an adjustable condylar pad that act as a corrective force. In more recent designs, a lengthening adjustment has been added to the proximal upright that allows for an angular shifting of the forces to create the offloading moment.

Studies have shown that the offloading forces exerted by these devices are successful in relieving pain in those patients with uni compartmental osteoarthritis during weight bearing activities (2,3,6). Although these designs have been successful, many times there is a certain degree of intolerance to the unloader knee orthosis that is experienced by the patient. This intolerance is typically due to a higher concentration of pressures being exerted by the strap or condylar pad, which can limit duration of use. As offloading adjustments are being made in the double upright designs, the frame configurations of the unloader orthosis do not follow a natural progression as oriented to the long axis of the leg when viewed in the coronal plane. As the corrective forces are applied to obtain the optimal offloading moment, there is an inability to distribute these forces proportionally through the leg. This leads to an inability to better match the center of rotation of the leg as viewed in the coronal plane, which can further limit compliance. In addition, the three points of pressure used in both designs are applied by laterally or medially shifting the femur and/or tibia to offload the affected compartment. This lateral or medial shift causes a certain amount of shear to the mechanical knee joint(s) resulting in a varying degree of binding with in the mechanical joint(s). This mechanical binding can further restrict the patients ability to freely flex and extend there knee during various activities of daily living. This shifting of the uprights and binding of the mechanical joint(s) that are felt by the patient can decrease the ability for the patient to comply with a single or double upright unloader knee orthosis.

The Varum Valgum adjustable stress (V-Vas™)[*V-Vas™ is fabricated and distributed by Anatomical Concepts Inc., Poland, OH 44514-3250] custom unloader knee orthosis is a new concept in treating patients who present with medial or lateral compartmental arthropathies. Its custom design incorporates several unique features that increase the effectiveness and compliance for the patient who is in need of an unloader orthosis. Instead of using a narrow frame as seen on most all double and single upright designs it uses a total contact cuff on the thigh and tibia along with a unique adjustable self aligning polycentric joint system to create four points of pressure instead of three. With two points of pressure being applied as a counter force (located at the proximal and distal ends of the thigh and tibial cuffs on the affected side of the leg) and two points of pressure applied as the corrective force (located at the distal and proximal ends of the thigh and tibial cuffs respectively on the non affected side of the leg) to offload the affected compartment, there is no need for a condylar pad. As compared to the single upright design, the use of a counterforce strap is not necessary once again, due to the four points of pressure used to create the offloading moment. Its self aligning polycentric hinge design, features an efficient and effective means of linearly adjusting the varum or valgum angle (depending on which compartment is affected) without causing mechanical joint binding. This is a very practitioner friendly design due to the mechanical joint never needing re-squared. The VVas ™ has been very effective in the clinical management of patients with symptomatic medial compartment osteoarthritis. Other successful applications include, lateral compartment osteoarthritis on patients with no abnormal genu valgum alignment up to 30º of semi flexible genu valgum, non-operative tibial plateau fractures, failed hardware or reconstruction of the tibial plateau, tibial plateau and or femoral condyle spacers and post total knee arthroplasty.

The V-Vas™ is currently available in a custom design. The finished design consists of a polypropylene constructed posterior opening thigh and tibial cuff that include a corrugation, to increase transverse plane integrity. The V-Vas™ is secured to the extremity via a Velcro® popliteal strap, wrap around thigh and distal tibial cuff straps. The thigh and tibial cuffs are connected via a medial and lateral self aligning polycentric knee joint. One of the self aligning joints (placed on the affected side of the leg) has the ability to be lengthened linearly at its proximal and distal ends. The lengthening can be adjusted proportionally or disproportionately proximally (thigh) and/or distally (tibia) to accommodate varying proportions of soft tissue compression. This linear (lengthening) adjustment is achieved via a counter clockwise rotation of the adjustment screw. The opposing self aligning polycentric joint in the V-Vas™ design is static and functions as a fulcrum to the adjustable self aligning polycentric joint. This ability to lengthen the upright in a linear motion allows for an anatomically correct varum or valgum force to be applied to the femur and tibia through the soft tissues via the thigh and tibial cuffs respectively. The ability to lengthen the adjustable upright either proportionally or disproportionately is how the optimal offloading moment is achieved. The self aligning joints in combination with the linear adjustment are at the heart of the uniqueness of the V-Vas™. The joint construction consists of a polycentric design that allows for a medial or lateral pivoting motion in the coronal plane. This pivoting motion is achieved through the use of two spherical bearings that are at each axis within the joint head. This design feature not only allows for uninhibited flexion and extension to 180º, but an ability to compensate for varying degrees of angulations as viewed in the coronal plane within the joint head. This ability to pivot accommodates the elongation of either the proximal and/or distal upright, resulting in the self aligning feature. Suspension and anti-migration are accomplished through a removable silicon laden popliteal strap pad and tibial cuff pad. Comfort is further achieved through a removable thigh cuff liner.

In a resent case study of a 51 year old male, 5'11" tall and weighing 220 pounds. The radiographs of the treated leg showed a 5º or 5 mm improvement in lateral condyle separation while fully weight bearing, using the V-Vas™ (Figure 1) versus the radiograph of the nontreated leg (Figure 2). This offloading moment of the lateral compartment allowed this patient to ambulate with minimal pain while wearing the orthosis.

Figure 1. Shows an increase in the lateral condyle space of 5º or 5mm in a full weight bearing position while wearing the V-Vas™ offloading custom knee orthosis.	Figure 2. Shows the collapsed lateral condyle space in a full weight bearing position when no orthotic intervention is used.

There are many design options available to those patients needing offloading knee orthoses. We know from reviewing literature that offloading orthoses are both ethical and very effective. There application will minimize use of medication, delay arthroplasty in the younger patient and control pain in those patients with co morbidity. They are also used as a pre-operative tool or post operative tool to determine the success of a surgical technique or offloading of the operative compartment respectively. As health care professionals we should strive for optimal outcomes when recommending various designs. Compliance, effectiveness and efficiency in design are all key factors in achieving this optimal result in the current healthcare arena. The unique features in this new design are an efficient and effective alternative used to achieve optimal results.

References

1. Finger S, Paulos LE. Clinical and Biomechanical Evaluation of the Unloading Brace. Journal of Knee Surgery 2002; 15: 155-159.

2. Pollo FE, Otis JC, Backus SI, Warren RF, Wickiewicz TL. Reduction of Medial Compartment Loads with Valgus Bracing of the Osteoarthritic Knee. The American Journal of Sports Medicine 2002; 30:3: 414-421.

3. Self BP, Greewald RM, Pflaster DS. A Biomechanical Analysis of a Medial Unloading Brace for Osteoarthritis in the Knee. Arthritis Care Research 2000; 13:4: 191-197.

4. Draper ERC, Cable JM, Sanchez-Ballaster J, Hunt N, Robinson JR, Strachan RK. Improvement in function after valgus bracing of the knee. The Journal of Bone and Joint Surgery 2000; 82-B:7: 1001-1005.

5. Giori NJ. Load-shifting brace treatment for osteoarthritis of the knee: A minimum 2 1/2-year follow-up study. Journal of rehabilitation Research & Development. March/April 2004; 41:2: 187-194.

6. Nadaud MC, Komistek RD, Dennis DA, Anderele MR, Kubo MB. “In Vivo Three- Dimensional Determination of OA Brace Effectiveness: A Multiple Brace Analysis” from the written material for a lecture delivered at American Academy of Orthopaedic Surgeons 72nd Annual Meeting, 2005.