Osteoarthritis presents less commonly in the ankle than in other lower limb joints. This is, perhaps, surprising, as the stresses in the ankle are high and the joint surfaces area lower than in other joints. In the ankle OA is often, but not always, secondary.
- Post-traumatic arthritis. These patients are often younger and have only one joint involved. They may still hope to return to an active lifestyle including contact or extreme sports, which may have precipitated their injury in the first place, and may be intolerant of residual restrictions or discomfort. Some have quite significant deformities or bony defects that preclude replacement or simple reconstruction; may have had open fractures, wound problems or infected pin tracks that predispose to infection; or nerve injuries or regional pain syndromes that limit the improvement that can be expected from treating their arthritic joints. In Saltzman’s (2005) series 70% of ankle arthritis was post-traumatic and in Valderrabano’s (2009) 78%.
- Rheumatoid arthritis and other inflammatory diseases such as psoriatic arthritis, where the inflammatory component has burnt out leaving a damaged joint. These patients often have several joints involved, and may have other joint replacements. They tend to be less mobile and more disabled than patients with other conditions listed below. Rheumatoid disease can affect immunity, renal and pulmonary function and the patients are often anaemic. Many second line drugs also affect immunity and may affect wound healing and increase the risk of infection after surgery. 12% of Saltzman’s (2005) cases were rheumatoid; 13% of Valderrabano’s patients had RA or other systemic arthritides
- Primary osteoarthritis. This is probably commoner than formerly believed. Some of these patients have monoarticular or oligoarticular disease, remain fairly active and expect to continue doing so. Others have multiple joint involvement and in this sense are more like rheumatoid patients, but without the systemic effects. 7% of Saltzman’s (2005) patients and 9% of Valderrabano’s (2009) had primary OA
- Intra-articular disease such as osteochondritis dissecans, osteonecrosis of the talus or synovial chondromatosis. Clinically these patients resemble the primary osteoarthritics but may have had several previous procedures, open or more commonly arthroscopic, which may leave complications and limit future options.
- Arthritis secondary to instability and/or foot deformity. A few patients have arthritis related not to an acute injury but to chronic instability; persistent ligamentous instability is likely to preclude ankle replacement. Major foot deformities such as pes cavus or severe flatfoot, or proximal malalignments such as a malunited tibial fracture, can lead to asymmetric loading of the ankle and/or ligamentous instability and subsequent arthritis. The abnormal biomechanics can preclude an ankle replacement, or require a preliminary realignment or stabilisation.
- Septic arthritis . The joint may be destroyed by sepsis which then limits the reconstructive options. These patients often require complex reconstruction.
- Type 1 – isolated ankle arthritis (52% of cases (Krause 2010))
- Type 2 - ankle arthritis with intra-articular deformity, ankle instability or a tight heel cord (12%)
- Type 3 – ankle arthritis with extra-articular deformity (8%)
- Type 4 – any of the above with subtalar, talonavicular or calcaneocuboid arthritis, as defined by pain, limitation of movement or radiographic change (28%)
- Type 1 – ankle fusion or replacement with no additional procedure other than syndesmosis fusion (to allow for the Agility replacement)
- Type 2 - ankle fusion or replacement with additional soft tissue procedure requiring a second incision
- Type 3 - ankle fusion or replacement with additional osteotomy or midfoot fusion
- Type 4 - ankle fusion or replacement with additional hindfoot fusion
- Check other joints and limb alignment
- Look at the gait - most patients have an antalgic gait
- Examine the skin and soft tissues carefully for the effects of previous surgery, injury or infection
- Check the alignment of the tibia to the hindfoot, the midfoot and the forefoot. What is the overall foot shape? If there is malalignment, is it correctable or fixed – it may be correctable at some levels but not at others.
- Palpate for tender areas, synovitis, effusion and loose bodies. If there is anterior tenderness, dorsiflex the ankle while pressing in the tender area (the Molloy impingement test), looking for an impingement lesion.
- Assess the range of ankle motion; check that any dorsiflexion/plantarflexion is in the ankle rather than the midtarsal joint.
- Establish whether movement of each relevant joint reproduces the patient’s pain, either in mid-range or at the extremes of movment
- Perform the anterior draw and talar tilt tests for instability.
- Check what movement remains in the subtalar and midtarsal joints.
- Assess circulation, sensation and power.
- The patient could try non-surgical treatment with a reasonable hope of controlling symptoms, at least in the short to medium term
- The patient has exhausted non-surgical treatment and some form of surgical treatment could be considered electively
- There is evidence of some serious underlying problem, usually infection, which needs to be tackled urgently
- The arthritis is relatively early, with some residual joint space and adequate alignment and bone stock - arthroscopic debridement may be worth considering, or, if there is deformity, osteotomy of the calcaneum or distal tibia
- There is end-stage arthritis which would require arthroplasty or fusion
- There is a complex problem which may require additional procedures such as debridement, massive bone grafting, multiple reconstructive fusion or the use of an Ilizarov frame
- Advice and reassurance on the relatively benign natural history of osteoarthritis, hurt doesn’t mean harm, keep fit and active etc
- Simple analgesics, NSAIDs, medium strength analgesics
- Improved control of inflammatory arthropathies, often with second-line drugs
- Some patients find it useful to wear boots rather than shoes, and sometimes splints or braces are useful to control symptoms
The Canadian Orthopaedic Foot and Ankle Society have developed a classification of the complexity of ankle osteoarthritis pre-operatively (Krause 2010) and for the procedures required postoperatively (Krause 2012). Krause (2010) reported inter-observer kappa of 0.62 and intra-observer 0.72 for the pre-operative classification and (Krause 2012) for the post-operative classification 0.89 and 0.87.
Most patients present with pain in the ankle. Sometimes it is described in the posterior foot or midfoot, or up the leg. Radiation above the mid-tibia should make one suspect proximal problems. Some patients complain the ankle locks or gives way, which may be due to a loose body but usually just represents attacks of severe pain with reflex inhibition of the supporting muscles. Midfoot pain may also arise from OA of the talonavicular, calcaneocuboid or lesser tarsal joints. It can be difficult to work out which joint(s) the pain is coming from – careful localisation of symptoms and individual joint examination are probably most useful.
It is important to find out what has already been tried. It is quite common to see a patient referred for an ankle fusion or replacement who is not even taking regular analgesics. There may be several non-surgical options to explore, or the patient may have tried all these and needs counselling about definitive surgery.
As noted above, patients with arthritic ankles may have other joints involved, which may affect the surgical option and likely outcomes. Others have had a severe or repeated injury or infection, which may have affected their soft tissue envelope or left troublesome scars or nerve problems. A history of deep infection will restrict definitive surgical reconstruction possibilities – almost certainly to a fusion, possibly with an Ilizarov or other external frame.
Cigarette smoking increases the risks of ankle non-union by at least three times, and may affect wound healing after any procedure.
The main investigation is a standing AP and lateral radiograph of the ankle. This will allow assessment of remaining joint space, spurs and loose bodies. If there is malalignment, a standing hindfoot alignment view will show at which level – ankle, subtalar or both – the malalignment is occurring. Plain radiography may show multiple arthritic joints and differentiation will normally rely on clinical examination and local anaesthetic injection. Other imaging is only required for specific indications.
Injections of local anaesthetic and/or steroid are commonly used to identify the likely source of pain. Khoury (1996) reported that injections were more useful than imaging, and correctly identified the source of pain in 20/22 patients. Contrast was used to confirm the placement of local anaesthetic. Carmont (2009) described multiple communications between tarsal joints, most commonly talonavicular-calcaneocuboid and ankle- subtalar, which calls into question the accuracy of diagnostic injection. Reach (2009) and Smith (2009) described ultrasound-guided injections in cadavers. Reach injected methylene blue int a variety of sites in the foot and ankle in cadavers; all were 100% accurate except 90% accuracy for the posterior subtalar joint. Smith injected coloured latex into the posterior subtalar joint of cadavers using ultrasound guidance by the anterolateral, posterolateral and posteromedial approaches. All injections placed latex into the joint; the lateral approaches also placed latex outside the joint in 25% while the posteromedial approache leaked in 8%. Clinical studies of ultrasound are required to assess this promising technique.
Where there is loss of bone stock or complex anatomy post trauma or infection a CT can be helpful. SPECT-CT (Pagenstert 2009) has been reported as a highly accurate method of identifying pathology in ankle and hindfoot OA, but is not yet widely available.
MR will show joint surface lesions such as osteochondritis dissecans, and soft tissue abnormalities including infection and sinuses.
If there is osteonecrosis, usually of the talus, MR will show the extent of the abnormality, which will help surgical planning, but an isotope bone scan is required to show how much revascularisation has occurred.
Standard blood tests may be required to rule out inflammatory arthropathy, gout or residual infection.
After history, physical examination and appropriate investigation, it should be possible to decide whether
If surgery is appropriate:
Most patients presenting with arthritic ankles can be managed with simple measures:
Steroid injections are often helpful on an empirical basis, although there is no good evidence base for their use and in other joints they may not be much better than placebo. In general, Kraus (2010) found the anterolateral portal slightly more accurate for ankle injection, with a 86.1% success rate compared with 77.5% for the anteromedial portal, although the difference was not statistically significant.
Hyaluronan supplementation injections have been described in other joints. Three small RCTs have been reported in the ankle (Salk 2006, Karatosun 2008, Cohen 2008). Salk and Cohen compared hyaluronate to saline injections in 17 and 28 patients respectively. The main outcome measure was the Ankle Osteoarthritis Scale. In each case there was a significant improvement in AOS in hyaluronate-treated patients, but this also occurred after saline injection and a significant difference between treatment groups occurred only at one time-point in one trial. Karatosun compared hyaluronate injections to exercise therapy in 30 patients. Again, both groups improved on the AOFAS ankle score, and there were no significant differences between the groups.
Chang (2012) carried out a meta-analysis of the existing trials and considered that the evidence favoured hyaluronan in the ankle over placebo and exercise, although confidence limits of treatment effect included zero. Colen (2012), in the course of a meta-analysis of hyaluronan in various joints, felt that the evidence in favour of viscosupplementation was stronger in the ankle than elsewhere, but that it was not significantly better than comparator treatments.
Larger trials are required to assess the real significance of the differences found. At the moment hyaluronate should probably be used only in the context of such trials.
Surgery is an option where non-surgical treatment has failed to control the patient’s symptoms and they are seriously affecting the patient’s activities of daily living, work and sleep.
Can be useful where the joint is reasonably well preserved, especially if the main problem is impingement from synovitis or spurs, or loose bodies. Arthroscopic debridement for impingement had a 75% success rate at 5 years in the presence of spurs, but only 50% with loss of joint space (Tol et al 2001). Ogilvie- Harris et al (1995) found limited improvement in about 2/3 of 27 patients. Choi (2012) found a significant improvement in VAS pain scores and AOFAS ankle scores that peaked at 6 months. At 2 years nearly 50% of patients had a failed outcome, although average scores were still better than outcome across the group.
An Ilizarov external fixation frame is applied across the ankle and a distraction force applied. The frame is articulated to allow active joint movement. Useful improvement in pain and movement have been reported (Marijnissen et al 2003). Weightbearing radiographs suggest that joint cartilage thickness is regenerated. This technique requires complex apparatus and specialised staff. Tellisi (2009) reported 23 patients who had distraction with a circular frame that allowed weightbearing and ankle movement. 5mm distraction was applied for 12 weeks. At a mean of 30 months follow-up the mean AOFAS score was 74/100. Pain scores improved in 21/23 patients and there was some improvement in SF-36 scores but this did not reach statistical significance. Patients with pre-operative equinus gained dorsiflexion, but the average range of movement of the group overall did not change.
Saltzman (2012) randomised 40 patients to static distraction or distraction with motion. All patients had an initial ankle debridement. This trial was underpowered compared with the initial power calculation. However, both groups showed an improvement in ankle osteoarthritis scores that was maintained at 2-year follow-up. Patients who had motion in the frame had significantly better scores from 6 months onward.
Distal tibial malalignment may be secondary to injury, intra-or extra-articular or involving the growth plate; or it may be an intrinsic deformity. Realignment is an option where the joint is reasonably well preserved – an arthroscopy may be required to check. Where the joint is severely arthritic an arthrodesis or replacement is more appropriate.
Until recently this was the only real option for end-stage ankle arthritis of whatever aetiology. The traditional British method was that of Charnley with a destructive anterior transverse approach and external fixation with a semi-stable frame. This had a high incidence of infection and non-union. Arthroscopic fusion has deveoped to the point where it is now the standard techniue for most foot and ankle surgeons.
Arthroscopic ankle fusion is normally performed with the patient supine using anterior portals. The technique of forming the portals is described in the section on arthroscopy.
Open fusion can be done using anterior, posterior and lateral approaches. A short medial arthrotomy is sometimes a useful adjunct to a lateral approach, although an extensile medial approach can be used to access talonavicular, subtalar and ankle joints. The lateral approach exposes the lateral malleolus, which can be excised and morcellised for graft, or removed, decorticated and attached as a large graft at the end. An alternative technique for graft harvest is to use an acetabular reamer to remove the lateral malleolus. The superficial peroneal and sural nerves, and their communicating branches, are at risk.
The anterior approach is the same as for ankle replacement, between tibialis anterior and EHL and exposing back to both malleoli. The deep peroneal/dorsalis pedis bundle is at risk, and the intermediate branch of the superficial peroneal nerve can cross the incision.
Many series of open ankle fusion have used flat cuts with a power saw or osteotome to excise the joint. Others use techniques to increase stability and congruency, such as anatomical resection of the joint surfaces in the manner of arthroscopic fusion, or a chevron cut (Kopp 2004). Preservation of the malleoli increases stability.
In arthroscopic fusion, synovitis and spurs are cleared to expose the joint line. Curettes and burrs are then used to remove the remaining articular cartilage and freshen the subchondral bone so that multiple bleeding points are seen. It is important to clear all the way to the back, usung the FHL tendon, usually seen through the posterior ankle capsule, as a landmark. It is also important to clear the gutters, the malleoli and the medial and lateral surfaces of the talus and to ensure that no osteophytes on the talus prevent compression of the talus into the mortise. Once preparation is complete, fixation is usually with two or three cancellous lag screws inserted over guidewires. Intra-operative check Xrays often show a gap between the joint surfaces, but as long as it is not too big and fixation is secure, the gap will disappear as healing progresses.
However the joint surfaces are prepared, the ankle should be positioned in neutral plamtar/dorsiflexion, 5 deg valgus and 5-10 deg external rotation (Buck 1987). Fixation in most series was with 2-4 cancellous bone screws. The stability of the fusion can be increased with an anterior or lateral plate, blade plate or ring fixator.
The ankle is normally protected with a backslab immediately after surgery and this is converted to a cast when the wounds are satisfactory. Where the construct is stable enough, partial to full weightbearing can begin quite early; we allow patients with arthroscopic fusions to bear weight to comfort at 2 weeks. There are a variety of regimes for reducing splintage, but no clear evidence of what regime is best to optimise fusion rates without spending unnecessary time in cast. Winson (2005) found that 12 weeks cast immobilisation reduced the non-union rate, but there has been no prospective confirmation of this finding.
Over 15 series of arthroscopic ankle fusions have been reported. The largest series is that of Winson (2005). 118 fusions were reported, of which 105 were followed clinically for a mean of 65m. 109/118 procedures fused at a mean of 12weeks. Most non-unions happened early in the series, and subsequently the authors immobilised all patients for a minimum of 12 weeks. Smoking was twice as common in non- unions. There were three superficial and one deep infection, one malunion and two pulmonary emboli. Winson recommended arthroscopic fusion even if the ankle was in valgus or varus provided the forefoot was plantigrade.
Gougiolias (2007), however, carried out arthroscopic fusions even if there was mortise deformity and the foot was not plantigrade, by excising bone from the mortise arthroscopically to align the ankle. 30/78 patients had a pre-operative coronal deformity of >15deg, but none had more than 3deg post-operatively. Five patients had simultaneous arthroscopic subtalar fusion. There were 5 delayed unions and 2 non- unions; time to union was 2months extra in smokers. There was one PE, one nerve injury and 6 patients had subtalar pain.
Overall about 600 arthroscopic fusions have been reported with a total fusion rate of 94%. Several series have commented on the quicker rate of union in arthroscopic procedures although this can be influenced by the intervals at which radiographs are taken, and all series diagnosed union on plain radiography rather than CT. Myerson (1991) noted a mean time of fusion of 8.7 weeks in arthroscopic versus 14.5 weeks in open fusions, while Nielsen (2008) noted that 90% of arthroscopic and 57% of open fusions were united at 12 weeks.
A study of patients 20 years after ankle fusion (Fuchs 2003) reported reduced SF-36 pain, physical functioning and emotional disturbance scores, and moderate Olerud ankle scores. Most patients wore customised footwear, but few had walking aids. All but one had returned to work. There was significant progressive OA in the other hindfoot joints. The surgery included more external fixation than would be expected in a current population, and most patients had what would now be considered mal-unions. Another study (Buchner et al 2003) reported little or no pain and restriction of activity in 92% of patients at an average of 9.3 years follow-up.
An independent study of fusion in OA (Anderson et al 2002) found that the true fusion rate was 80-89% but the clinical and radiological outcomes were not the same. In rheumatoid disease, Felix et al (1998) reported union in 96% of 26 ankles at 2-8 year follow-up, and no pain. Although many studies are quite old and use techniques that are uncommon now, the risk of non-union is almost certainly higher in open than arthroscopic fusion.
Arthroscopic versus open fusion
No RCT comparing arthroscopic and open ankle fusion has been reported. Townshend (2013) compared two prospectively-studied cohorts of patients undergoing ankle fusion. At one centre all fusions were done by a transfibular open technique, while at the other, all fusions were done arthroscopically. The open fusions had more primary OA, while the arthroscopic series had more post-traumatic OA, but otherwise the groups were comparable. 1/30 patients in each group had a non-union. The arthroscopic group had significantly better Ankle Osteoarthritis Scores at 1 and 2 years; SF36 was better in the arthroscopic group but not significantly. Hospital stay was a day less in the arthroscopic group and this was significant.
The arthroscopic technique is now the standard method of fusing the ankle unless there is severe deformity, bone loss or revision surgery. However, it requires advanced arthroscopic skills. It is feasible in patients whose soft tissues would not be suitable for open surgery.
Cheng (2003) reported 18 revisions, 10 of which were for non-union, 7 for mal-union and one for infection. Screw fixation was used in all but one case and 17/18 fused including the infected case, taking a mean of 4.8months. At a mean follow-up of 40months the mean AOFAS score was 71/100 (range 38-86). Easley (2008) reported 45 patients including 8 infected cases. 11 had screw fixation, 12 had a tibiotalocalcaneal fusion with a nail and 22 with bone loss or infection had a ring fixator. At a mean 50 months follow-up, 40/45 were fused, 5 of whom had required revisions. There were 5 amputations and 4 malunions and most complications were in the patients who had the ring fixators.
Total ankle replacement
Replacement of the ankle has been around for over 30 years. However, early prostheses did not reproduce the biomechanics of the ankle well and had a very high failure rate. Second-generation prostheses from the late 1980s onward introduced improved engineering, often with three components.
Hindfoot fusion to correct deformity or treat adjacent arthritis does not affect functional scores in comparison to isolated ankle replacement, although range of movement is less after adjacent fusion (Kim 2010). Cavus deformity (Jung 2013) may also need correction.
Results in OA and RA are similar (Kofoed 2004, Wood and Deakin 2003). Bai (2010) reported no difference between results in post-traumatic and primary OA, although there were more complications in the post- traumatic group. Ankle prostheses also seem to be best uncemented; the long term results of the STAR ankle have been significantly better in the uncemented design (Kofoed 2004).
Bilateral replacement can be carried out at the same procedure. However, Barg (2010) found post- operative pain scores were higher in bilateral that unilateral replacements at six months, although this difference vanished at 1 year. Recovery appears to be more prolonged after bilateral replacement.
Clinical series of ankle replacement
Gougoulias (2009) published a systematic review of 13 series amounting to 1105 ankle replacements, of which the Agility, STAR and Hintegra were commonest. Only 4 studies had more than 10 years’ follow-up. Survivorship rates were variable, satisfaction rates varied from 79-97% but 23-60% of patients still had some pain. Zaidi (2013) reported a systematic review of nearly 8000 ankle replacements, in which 10-year survival was 89%. The annual failure rate was three times as high in registries (the overall population) than in designers' series. 23% of patients had peri-prosthetic lucencies at an average of 4.4y. AOFAS score showed large improvements but few other, validated, scores were reported. Subtalar OA progressed in 19-59% of ptients, although this outcome was reported on only 3 series.
The Swedish arthroplasty register figures (Henricson 2007, 2011) found a 5-year survival of 78%, which improved to 86% after the first 3 cases, and a 10-year survival of 69%. The Nowegian register (Fevang 2007) reported 5-year survival of 89% and 10-year of 76% in mostly STAR ankles. The Finnish register (Skytta 2010) reported a 95% 5-year survival in a 50% rheumatoid population using mostly AES and STAR ankles.
Wood (2009) reported the only RCT in ankle replacement, comparing 100 STAR ankles with 100 Buechel- Pappas ankles. The survival rates at 6 years were 955 for the STAR and 79% for the BP (the difference was not significant) In both groups survivorship was lower with increasing coronal plane deformity.These studies tend to highlight need for revision as the main outcome measure. At 12 years, the survivorship of the current cementless Buechel-Pappas implant was 92% (Buechel et al 2004), but clinical results were presented only as excellent 88%, good 5%, poor 7% (75 patients). Twelve-year survival for the STAR ankle was 95%, with a mean Kofoed ankle score of 91.7/100. The long-term survival rate is based on small numbers in each study.
The Wrightington series (Wood 2008), reported 200 ankles followed for a minimum of 5years and a mean of 7.3 years. The 5-year survival was 93.3% and the 10-year survival 80.3%. The mean AOFAS hindfoot score for pain improved from 0/40 pre-operatively to 35 at final follow-up and the functional score from 28/60 to 40. Complications and the learning curve are detailed.
As in the RCT with the BP ankle, survivorship was significantly lower in the presence of coronal plane deformity, and Wood recommends 15deg valgus or varus as the maximum for successful ankle replacement. However, Hobson (2009) reported 123 STAR ankles including 32 with coronal plane deformity of 10-30deg, mostly varus. Survival at 5 years was 86% for the neutral ankles and 75% for the deformed ankles, which was not a significant difference. Nine patients in the deformed group needed additional corrections – 6 calcaneal osteotomies and 3 lateral ligament reconstructions. Kim (2009) found that the results in varus ankles were the same as those in neutrally aligned ankles.
Failed ankle replacement
Like all joint replacements, failure occurs and may require revision replacement or fusion. Kessler (2012) found that the main risk factors for infection after TAR were previous surgery, low pre-operative AOFAS scores, long operative time and post-operative wound problems. Relatively few series have presented the management of failed ankle replacement (Spirt 2004, Anderson 2005, Kotnis 2006, Hopgood 2006, Doets 2010, Hintermann 2013)
Kotnis (2006) presented an algorithm for the management of failed ankle replacement focused on the presence of infection. 5/16 patients had revision arthroplasty, 10 had tibiotalocalcaneal fusions (one with an Ilizarov frame) and one had a below-knee amputation.
Hintermann (2013) reported the results of revision HINTEGRA arthroplasty. In 117 cases, 15 failed at a mean of 6.2yrs, giving an estimated 9-year survival of 83%. THE mean AOFAS score in surviving ankles improved from 44/100 pre-operatively to 72 at latest follow-up.
Hopgood (2006) and Doets (2010) reported salvage arthrodesis. Hopgood reported that when there was enough bone stock, tibiotalar arthrodesis with screws was uniformly successful. In the presence of more bone loss, tibiotalocalcaneal fusion was carried out with screws or a nail and was successfulin 9/15 patients. Doets reported higher union rates with blade plate fixation than with IM nailing, and in osteoarthritis rather than inflammatory arthritis. His overall union rate was 11/18, with two non-unions healing after revision.
Spirt (2004) reported secondary surgery after Agility ankle replacement, which was widely used in the USA but not in the UK or Europe. 24/33 failed replacements were revised, one was fused and eight had below-knee amputation.
Fusion versus ankle replacement
It is only appropriate to compare fusion and replacement for patients without major deformity, infection, bone loss or neuropathy – these would only be candidates for fusion. However, there have been no RCTs comparing replacement and fusion in patients in whom both would be an option. In addition, outcome measures in single-procedure series are so varied that it is difficult to compare them.
The only comparative study is that of Saltzmann (2009, 2010). This was an FDA approval study in which patients were assigned to STAR ankle replacement or open ankle fusion through a fibular osteotomy with screw fixation, according to the surgeon doing the procedure. There was also an open series of ankle replacements. The main outcome measure was the Buechel-Pappas ankle score. This improved by a mean of 40 pints for the STAR group and 26 points for the fusions, mainly accounted for by significant improvements in most of the function scores. However, there was no significant difference in pain relief or patient satisfaction. There were more intra-operative problems, nerve injuries and wound problems in the STAR group, but similar infection rates of 4.4% in the replacements and 7.6% in the fusions (all but one minor). The union rate in the fusions was 64/66 and there appear to have been 7/415 loose replacements at 24 months (this is not easy to work out), with one revision for wear and 4 mobile bearing fractures. At an average follow-up of 4 years the clinical results of TAR were similar to those of fusion (Saltzman 2010). However, the arthroplasty group showed better pain relief and more postoperative complications that required surgery.
A systematic review of the literature by Haddad et al (2007) found the overall reported results of both procedures to be similar, with about 70% satisfactory results after both procedures. The overall non-union rate for ankle fusion was 10% and the arthroplasty survival rate 77% at 10 years. There was more variation in results for arthroplasty. Kwon (2011) used a decision analysis method and found a small advantage for replacement that was stable despite varying some of the model’s assumptions.
Slobogean (2010) also found similar overall results for fusion and replacement. Esparragoza (2011), however, found a greater improvement in AOFAS scores after replacement than fusion. SooHoo (2007) and Krause (2011) reported more adverse events after replacement, but SooHoo also reported more subtalar fusions after fusion. None of these series differentiated between RA and OA.
Many surgeons tend to favour ankle replacement for patients with polyarthritis with a view to maximizing retained function and minimizing the risk of adjacent arthritis. While this is not based on strong evidence, it is clinically plausible.
Kinematics and gait
As might be expected, ankle fusion affects the range of motion and kinematics more than does replacement, and certain designs are closer to normal than others (Valderrabano et al 2004a,b). Gait analysis is much closer to normal in replaced than in fused ankles (Butcher 2004, Piriou 2008). Hence it is plausible that ankle replacements would place less stress on other joints, both in the tarsus and proximally. Nevertheless, this requires clinical confirmation.
Naal (2009) found that 2/3 of 101 patients were active in sports 4 years after ankle replacements. The commonest sports were swimming, cycling, fitness training and downhill skiing and the patients participated for an average of 4.4hr/week. 35% had radiolucencies around the tibial implant but this did not affect the likelihood of sports activity. Schuh (2012) found no difference in activity levels after replacement or fusion, although activity levels in both groups diminished after surgery.
There is not enough data to indicate whether fusion or replacement is to be preferred for patients in whom either procedure would be an option. At about 10 years clinical success rates appear similar. Ankle replacement probably has a small functional advantage but failure rates vary widely and there is a much higher rate of secondary surgery.
It is possible that the onset of OA in other joints reduces the success of fusion thereafter. The improved kinematics of ankle replacement probably reduce the wear on adjacent joints, and this could be important, particularly in patients with multiple joint pathology. The improved range of movement is anecdotally useful to patients, but there are no comparative studies.
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