Ankle Arthritis - Paul Baghla 13/6/2006

Aetiology : primary osteoarthritis of the hip/ knee is very common, but primary ankle osteoarthritis is actually quite rare. The majority of ankle arthritis is posttraumatic in nature, usually being the result of a previous fracture or ligamentous injury (younger population)

Less frequent causes of ankle arthritis include inflammatory/ septic arthritis, and neuropathic arthropathy.

Non-operative treatment : weight loss, activity modification, walking aids, braces, rocker-sole shoes in addition to nonsteroidal anti-inflammatory drugs (NSAIDs) and intra-articular steroid injections.

Viscosupplementation : paucity of literature on use of hyaluronic acid injection in arthritic ankle.   Salk et al 2006, Double-Blind controlled trial, 20pts GII+

according to Kellgren and Lawrence,   Randomized to 1 ml saline/ 1ml hyaluronate in 5 weekly injections. At 6 months both groups significantly improved, but hyaluronic acid group had more profound benefit.

Arthroscopic debridement : small numbers with respect to knee arthroscopy. Strecker et al. 2005 have looked at their experience of 358 ankle arthroscopies (178 pts) between 1988-97. 124 patients responded to questionnaire; 11%, excellent, 46% good, 22% fair and 21% poor. 22% required further surgery (denervation, repeat arthroscopy, arthrodesis,). Best results for focal arthrosis, osteophytes impingement, soft-tissue impingement, loose bodies and synovitis.

Arthrodesis : gold standard for its predictability and its durability along with high degrees of patient satisfaction. 90% good/excellent results at 10 years (Morgan 1985 jbjsA)    Adjacent subtalar and Chopart joint arthritis, which develops following ankle arthrodesis, remains one of the primary concerns with this procedure. Coester et al 2001published 23 year f/u post arthrodesis (internal & external fixation).   Also poor gait analysis/ function.

Arthroscopic ankle arthrodesis : No randomised control trial. Two papers looking at the outcomes of arthroscopic ankle fusion were published during the last year. Winson et al. reported on 118 fusions. Their average time to fusion was 12 weeks (range 6–20) with 7.6% of cases going on to nonunion. While 94 of their cases had little or no malalignment (<10 ^o ) , they included in their series patients with deformities of up to 28 ^o varus and 22 ^o valgus.

Ferkel and Hewitt 2005 also reported on their experience with 35 arthroscopic ankle

arthrodeses with average follow-up of 72 months. Union rate was 97% with an average time to union of 11.8weeks. Two cases required external bone stimulation to achieve union while one case persisted to nonunion. While this procedure has often been criticized because of its learning curve and the operative time required, these results certainly compare favourably to more traditional open ankle fusions.

? ‘cherry-pick’ the least problematic healers from pool of patients for fusion ? high success rate secondary to selection bias?

 
Ankle Arthroplasty :

1970’s

Initial reports from first generation prostheses: 346 arthroplasties, good or fair results were reported in 83% and failures in 17% at a mean follow-up of less than 5 years (RA / low physical).   Consequently indications were relaxed to include young and high activity

 
1980-90’s

However with longer follow up (>5 years) most series of TAR showed poor long-term. Failure occurred in 35% to 76% of arthroplasties.  

Largerst series Kitaoka et al. (1996), 204 primary Mayo TAR’s implanted between 1974-88.   143 patients were evaluated (160 arthroplasties) for an average of nine years (range 2-17 years). Thirty-one ankles had good results, 35 had fair results, and seventeen had poor results. Failure, defined as removal of the implants, occurred in 57 arthroplasties. Adequate preoperative and follow-up radiographs were available for 101 ankles (89 patients). There was evidence of loosening in eight (8%) tibial components and 58 (57%) talar components. Reoperation rate 66 of the 160 ankles. Authors no longer recommended TAR with the constrained MAYO implant, due to the high rates of complications and reoperations.

 
Design Challenges :

• Limited soft tissue envelope, wound problems are problematic
• Forces at the ankle are very large and yet the surface area for prosthetic support is small, therefore difficult fixation.
• Eccentric bone quality at the distal tibia therefore prosthesis settles laterally into softer bone
• Polyethylene needs to be sufficiently thick to maintain its integrity but that requires a larger bone resection, which weakens bone support

  Failure from 1 ^st generation prosthesis:

  2 component- Excessive bone removal- implant subsidence

Constraint behaviour- too rigid-loosening

Methyl methacrylate cement fixation

nonanatomically shaped components

Inadequate surgical instrumentation-. poor implant position/ malleoli   fractures

 
Two-Component, Fixed-Bearing Design

Agility ankle system (DePuy). Only TAR which has FDA approval. Semi-constrained.   Requires distal tibio-fibular syndesmosis fusion to provide a stable platform for the component. Tibial component has fixed polyethylene bearing. Talar component is narrower than mortise- allowing translation/ coronal and axial rotation.

Largest series June 2004 by Knecht et al. average follow-up of 9 years, 132 TAR’s in 126 patients. 33 died, 14 revised, 1 BKA (unrelated cause?) in patients .>90% good/excellent, 19% progressive subtalar arthritis, 15% talonavicular arthritis, 8% had a syndesmosis nonunion.

Three-Component, Mobile-Bearing Designs

With every step, heel-strike imparts a powerful postero-anterior translational force which acts on the anterior aspect of the tibial component. This force will weaken the anterior tibial cortex and make the tibial component tilt backwards and downwards. This will happen regardless of the fixation technique used, and has been seen even with large central stems.   As a rule, this complication will occur within one to two years from implantation

The use of a mobile bearing insert, converts shear and torque forces into translational movement of a meniscal component cf unicondylar knee

It also makes the anatomical centres of rotation of the tibia and the talus match as the joint goes through its range of flexion and extension. A congruent (2 component) ankle design without a mobile bearing cannot produce this variation: Even though the two curvatures are the same, the anterior or posterior positioning of one component with regard to the other will lead to a loss of correspondence of the anatomical centres of rotation. This, in turn, will lead to eccentric wear, depending on tibial component position.

Examples include the Scandinavian Total Ankle Replacement (STAR), Hintegra total ankle (Newdeal SA, Lyon, France) & LCS/ Buechel-Pappas Ultra [Endotec, South Orange, NJ]

Recent meta-analysis of these prostheses revealed an overall 5-year survival of 90.6% (Stengel D 2005).   Overall range of motion of ankles in this study improved by an average of 6.3 ^o (range 2.2–10.5 ^o ) after arthroplasty. Secondary procedures were required for one in eight patients (12.5%) and overall rate of conversion from arthroplasty to fusion was 6.3%.

Biomechanical considerations

Some ankle replacements require a window in the anterior tibial cortex for their insertion. The anterior tibia plays a vital structural role especially in dorsiflexion. Blaimont et al, has demonstrated this biomechanical behaviour using starin gauges on the ankle under weight-bearing conditions.

(a) neutral or plantarflexion-uniform compression, midline weight-bearing axis, and   full joint congruence

(b) dorsiflexion- eccentric anterior loading, anterior weight-bearing axis, joint incongruous.

the distal anterior tibial cortex is   vital especially under conditions of single-limb weight-bearing during heel strike, when the foot is dorsiflexed

Axis of rotation: tradaitional transmalleoloar axis. Dorsiflexion associated with eversion and supination. Different axis for PF and DF 37 ^o   Large variation between subjects esp in saggital plane, however axis pass through centre of talus consistently.   Also rate of axis change is very variable from smooth to abrupt. (lundberg 2004) difference in coronal plane.

Joint distraction for ankle osteoarthritis

After arthroscopic debridement of the joint, a circular external fixator is applied across the ankle and the ankle joint is distracted about 5 mm. The patient is then allowed to weight bear with the fixator during the following 3 months. Experience has shown that continued clinical and radiographic improvement persists for several years after removal of the frame. Experimental evidence exists in animals that cartilage restoration may occur. Little such literature exists in humans. The Dutch group who have pioneered this technique have reported promising medium-term results [Ploegmakers J 2005]. After a follow-up of seven years on 22 patients, 73% reported continued improvement while 27% were treatment failures. While these results are exciting, the mechanisms of joint repair are hypothetical and remain poorly understood.

References