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Convex medial laxity may determine use of constrained prosthesis
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Convex medial laxity — not valgus angle severity as previously thought— increased the use of constrained prostheses in patients undergoing total knee arthroplasty.
“The key factor to determine the choice of a constrained [total knee arthroplasty] TKA is first the presence of laxity in the medial side, not only the valgus angle,” Gilles Pasquier, PhD, surgeon in the Orthopaedics and Traumatology Department at Hospital of Lille in France, said during his presented at the 12th EFORT Congress, held in Copenhagen, Denmark.
“Other factors, as a low patellar height or an elevated posterior tibial slope, when associated, potentiate this possible prosthetic switch (to higher constraints) and should make surgeons aware, in these situations, of encountering difficulties when establishing ligament balance,” Pasquier and his colleagues wrote in their study abstract.
Ligament balance is difficult to achieve when implanting a TKA in valgus knees, causing some surgeon to use constrained devices. Pasquier and colleagues evaluated the possibility of establishing the best preoperative criteria to predict the indication for use of a constrained TKA design.
Indication evaluated
The researchers conducted a retrospective study to analyze 93 consecutive total knee prostheses that were implanted between 1996 and 2004 to treat patients with a valgus deformity of more than 5°. Full weight-bearing long axis anteroposterior views were performed preoperatively, according to the abstract. This showed that hip/knee angle ranged from 186° to 226°. The investigators found that 36 knees had more than 15° of valgus, and 19 knees had more than 20° of valgus.
The study results showed that 52 knees had preoperative laxity in the coronal plane of more than 10°; 14 knees had more than 5° laxity on the convex side; and, 21 had more than 10° laxity on the concave side, Pasquier said.
In addition, 26 out of 93 TKAs used constrained prostheses. The other TKAs were regular posterostabilized prostheses.
‘Best argument’ for use
Factors that distinguished the selection of a constrained prosthesis were: valgus severity as measured by hip/knee angle, increased posterior tibial slope, low patellar height, and the “best argument” was the severity of laxity in valgus, according to Pasquier.
Among all these factors, “odds ratio analysis showed only one independent factor — laxity in valgus — which was really a positive factor,” he said. “The probability of implanting elevated constrained prosthesis was measured by two for each one degree increment of laxity in valgus.” – by Tara Grassia
Reference:
- Migaud H, Amzallag M, Pasquier G, Girard J, Gougeon F. Total knee arthroplasty in valgus knees: Is it possible to predict the indication for a constrained design regarding ligament balance? Presented at the 12th EFORT Congress, June 1-4, 2011. Copenhagen, Denmark.
- Gilles Pasquier, PhD, can be reached at the Orthopaedics and Traumatology Department, Hospital of Lille, Lille, France; email: gpasquier@nordnet.fr.
- Disclosure: Pasquier and his associate authors have no relevant financial disclosure.