Securing tibial component, adequate pressurization among concerns for mini TKA

Researchers found more complications early in the study, which may suggest a steep learning curve.

As interest increases in minimally invasive total knee arthroplasty, a new study warns of potential tibial component loosening.

In a study of their first 1000 consecutive minimally invasive total knee arthroplasties (TKA), Peter M. Bonutti, MD, and colleagues noted 20 reoperations. Surgeons performed 12 arthroscopic reoperations for patella-femoral crepitus. “We also found that there was retained cement, some hypertrophy in the notch, and loose fragments were identified,” Bonutti, founder of the Bonutti Clinic in Effingham, Ill., said during his presentation at the American Academy of Orthopaedic Surgeons 73rd Annual Meeting.

They also performed eight open procedures for conditions including a loose tibial component, late infection and a subluxated patella. “Tibial components are key and we need to look at the alignment,” Bonutti said. “Clearly, cement pressurization and fixation are major concerns.”

The researchers examined five-year data on 820 patients that underwent mini TKA. The study included unilateral and bilateral patients and those with a body mass index of less than 32. All procedures included a less than 12-inch initial incision and a mid-vastus approach. Surgeons also avoided patella eversion. After sliding the patella, surgeons sequentially performed tibial, femoral and patella osteotomies.

At six weeks postop, surgeons manipulated 25 knees with less than 95° of motion. “Two patients later had an open revision to increase the range of motion,” Bonutti said. Radiographic results also revealed six tibias with greater than 3° varus, he said.

The researchers also discovered 20 reoperations. “The major concern from this analysis was tibial component loosening, which may be related to decreased exposure and possibly poor cement pressurization,” they wrote in their abstract. “Keel length reduction or modification may lead to an improvement in survival.”

Steep learning curve

The investigators also noted that most reoperations occurred early in the series, highlighting a significant learning curve. “The first 200 patients were where we had the most substantial complications, and this suggests that maybe the early instrumentation or the kind of instruments could also lead the learning curve to be more steep than we could understand,” Bonutti said.

In addition to new instruments, Bonutti cited incision length and decreased exposure as variables in the learning curve. “We recommend that if you do this, look at an evolutionary approach,” he said. “Change only one variable at a time and critically examine all of your patients.”

He suggested avoiding extensive soft tissue pressure and safeguarding against crepitus. “We believe that if you don’t evert the patella, there’s a risk that the remaining part of the lateral meniscus or some of the fat pad, which can later hypertrophy, can cause damage,” Bonutti said. Finally, he underscored the importance of tibial component positioning. “So be cautious about appropriate cement pressurization, cement technique and cement removal,” he said.

For more information:
Bonutti PM, Mont MA, McMahon M, et al. Minimally invasive total knee arthroplasty: pitfalls and complications. #141. Presented at the American Academy of Orthopaedic Surgeons 73rd Annual Meeting. March 22-26, 2006. Chicago.