The Impact of Foot and Ankle Deformity on TKA
All knee surgeons are aware of the importance of component alignment in total knee arthroplasty (TKA).
Equally as important is the role of foot and ankle deformities, particularly subtalar deformities, in TKA. If not corrected, these deformities can adversely affect the short- and long-term outcomes of an otherwise well-executed TKA. [1-3]
Craig S. Radnay, MD, from the Insall Scott Kelly Institute for Orthopaedics and Sports Medicine in New York, addressed lower extremity deformity as a cause of clinical failure of TKA at the ICJR East meeting.
To detect foot and ankle deformities when examining a TKA patient pre- and postoperatively, Dr. Radnay:
- Evaluates the patient’s stance, including limb length
- Checks for deformity of the hindfoot, midfoot, or forefoot, including shoe wear and muscle strength and tightness
- Watches the patient walk
He also orders a 3-joint standing radiographic, which is the “gold standard” for evaluating overall alignment of the lower limb through the hip, knee, and ankle.
The issue is, however, that the weight-bearing axis is based on the relationship of the hip and knee with the center of the talus. In reality, the main “shock absorber” at heel strike is below the talus, at the subtalar joint.
A primary deformity at the ankle can overload the knee and cause arthritis. More significantly, a patient whose hindfoot has chronically compensated for a deformity at the knee will typically have a lateralized weight-bearing axis . If this is not addressed, Dr. Radnay said, there is a risk of early failure of the knee replacement.
Foot and ankle deformities can be addressed with non-surgical and surgical treatments. Surgical treatments are technically challenging, require hardware and osteotomy or fusion to maintain alignment, and usually have long non-weight-bearing recovery periods. The goal is to provide a painless, plantigrade foot for activities of daily living and alignment that protects the TKA above.
Dr. Radnay described 4 types of deformities: pes planovalgus, pes cavovarus, Charcot neuroarthropathy, and ankle arthritis.
Patients with pes planovalgus, also known as “flat feet,” have fallen arches, pronation, and hindfoot valgus.Lateral displacement of the calcaneus occurs relative to its normal position under the talusThis causes a lateral shift of the tibiotalar contact area and the weight-bearing axis in stance, as well as increased valgus load on the knee, ankle, and subtalar joints. The patient may experience medial knee pain, patellar maltracking, lateral tibial stress, gastrocnemius contracture, postoperative flexion contracture, and increased anterior knee pain.
Gross et al  found that patients with pes planus were 1.3 times more likely to report knee pain and 1.4 times more likely to have tibiofemoral cartilage damage on MRI. Other studies have shown similar findings.
Norton  and Mullaji  showed how varus knee deformity is associated with valgus hindfoot, with most of the compensation in the hindfoot occurring at the subtalar joints.
The varus knee deformity can be corrected at the time of TKA surgery, but the hindfoot valgus deformity may persist and may cause early failure of the TKA, as shown by Meding.  The extra-articular planovalgus foot deformity causes valgus stresses and rotational imbalance in the knee that can lead to failure.
Treatment for pes planovalgus will depend on whether the deformity is flexible or rigid.
Pes cavovarus is the opposite problem; it involves excess supination in the ankle and foot. Pes cavovarus is forefoot- or hindfoot-driven. It causes medial displacement of the calcaneus relative to talus/ankle This leads to a medial shift of the tibiotalar contact area and weight-bearing axis in stance, increasing varus load on the knee. Pes cavovarus is treatable with a variety of surgical options.
Charcot neuroarthropathy affects 2% of patients with diabetes. It is characterized by lack of sensation and bony destruction with soft,weak bone, as well as soft tissue incompetence. The Charcot foot is difficult to treat with standard fixation – the surgeon will generally do whatever is necessary to restore a plantigrade foot. There is a high risk for surgical reconstruction in patients with Charcot neurarthropathy
The prevalence of severe ankle arthritis – mostly as a result of ankle injuries – is rising dramatically. The ankle joint is subject to multidirectional forces many times those in the knee: 4-7 times body weight with vigorous activity.
Standard treatment of ankle arthritis had been ankle fusion, but that caused many problems such as non-union, stiffness, gait changes, and persistent pain. The alignment achieved in the fused ankle can negatively affect the knee and, therefore, is a a concern for a later TKA.
In contrast, total ankle arthroplasty can preserve ankle motion, improve gait and function, and decrease stresses on hindfoot and midfoot, thereby decreasing strain in adjacent joints.
A concern for orthopaedic surgeons managing patients with knee, foot, and ankle issues is which deformity to address first.
The older literature recommended correcting hindfoot malalignment before performing a TKA to minimize stress on the knee implant.
Newer research, however, recommends a “proximal-to-distal” approach. With this approach, much of the hindfoot malalignment will be corrected by correcting the knee deformity. Chandler  found that hindfoot malalignment decreases by 50% post-TKA, and Mullaji  noted up to 31% change in hindfoot alignment after TKA.
In his practice, Dr. Radnay typically addresses the most symptomatic joint first. If the knee is the more symptomatic, the TKA is done after fitting the patient for appropriate orthotics or a brace. If the hindfoot is more symptomatic, he will do the appropriate procedure to reestablish foot/ankle alignment and then stage the TKA. If the patient has co-existing painful deformities, Dr. Radnay will address the knee first.
Lower extremity alignment is crucial to the long-term survival of TKA. Restoring the hip-knee-ankle mechanical axis improves TKA longevity and patient satisfaction. If hindfoot malalignment persists after TKA, Dr. Radnay said, it will lead to failure of the knee replacement.
Dr. Radnay’s presentation can be found here.
- Peter F. Sharkey, MD; William J. Hozack, MD; Richard H. Rothman, MD, PhD; Shani Shastri, MD; and Sidney M. Jacoby, BA. Insall Award Paper: Why Are Total Knee Arthroplasties Failing Today? Clin Orthop Relat Res. 2002 Nov;(404):7-13
- Anil Bhave, Michael Mont, Scott Tennis, Michele Nickey, Roland Starr and Gracia Etienne. Functional Problems and Treatment Solutions After Total Hip and Knee Joint Arthroplasty. J Bone Joint Surg Am. 2005;87-A:9-21.
- David J. Jacofsky, MD, Craig J. Della Valle, MD, R. Michael Meneghini, MD, Scott M. Sporer, MD, and Robert M. Cercek, MD. Revision Total Knee Arthroplasty: What the Practicing Orthopaedic Surgeon Needs to Know. J Bone Joint Surg Am. 2010;92-A no 5:1282-92
- K. Douglas Gross, David T. Felson, Jingbo Niu, David J. Hunter, Ali Guermazi, Frank W. Roemer, Alyssa B. Dufour, Rebekah H. Gensure, And Marian T. Hannan. Association of Flat Feet With Knee Pain and Cartilage Damage in Older Adults. Arthritis Care & Research Vol. 63, No. 7, July 2011, pp 937–944
- Norton A, Amendola A, Phisitkul P, et al. Correlation of knee and hindfoot deformities in patients with advanced knee arthritis. Poster presented at: 2012 Annual Meeting American Academy of Orthopedic Surgeons; February 7-11, 2012; San Francisco, CA.
- Mullaji A, Shetty GM. Persistent hindfoot valgus causes lateral deviation of weightbearing axis after total knee arthroplasty. Clin Orthop Relat Res. 2011; 469(4):1154-1160.
- Meding JB, Keating EM, Ritter MA, Faris PM, Berend ME, Malinzak RA. The planovalgus foot: a harbinger of failure of posterior cruciate-retaining total knee replacement. J Bone Joint Surg Am. 2005; 87(suppl 2):59-62.
- James T. Chandler, MD, and Joseph T. Moskal, MD, FACS. Evaluation of Knee and Hindfoot Alignment Before and After Total Knee Arthroplasty A Prospective Analysis. The Journal of Arthroplasty Vol. 19 No. 2 2004.