Clin Orthop Surg.  2016 Jun;8(2):157-163. 10.4055/cios.2016.8.2.157.

Analysis of Impingement between Patella Bone and Bearing Post in Cruciate-Substituting High-Flexion Total Knee Arthroplasty

• Chon J
• Lee B
• Shin S
• Jang G
• Jeon T

• KMID: 2412340
• DOI: http://doi.org/10.4055/cios.2016.8.2.157

Abstract

BACKGROUND
We investigated the causes of impingement between the patella bone and the bearing post during high flexion in cruciate-substituting total knee arthroplasty and proposed a treatment strategy.
METHODS
This prospective cohort study included 218 cases that had undergone cruciate-substituting total knee arthroplasty from February 2014 to January 2015; a single surgeon performed the operation using the same method without patellar resurfacing in all patients.
RESULTS
In these patients, the occurrence of impingement was determined by performing more than 120° high knee flexion after inserting a bearing perioperatively. The incidence of impingement was significantly associated with bearing design, femoral implant size, patella bone length, and patella inferior pole angle (p < 0.05). The impingement was resolved by resection of the lower articular side of the patella bone.
CONCLUSIONS
In the cruciate-substituting high-flexion total knee arthroplasty, impingement between the patella bone and bearing post was more common in patients with mobile bearing, small-size femoral component, and a long patella or a large inferior pole angle. In cases of intraoperative impingement between the patella bone and the bearing post, resection in the lower portion of the patella prevented impingement of the bearing with soft tissue or the patella by widening the space between the patella and the bearing post, which in turn prevented postoperative reduction in range of motion.

Keyword

Impingement; Patella; Bearing post; High flexion; Total knee arthroplasty

MeSH Terms

Aged
Aged, 80 and over
*Arthroplasty, Replacement, Knee/adverse effects/statistics & numerical data
Female
Humans
*Knee Prosthesis/adverse effects/statistics & numerical data
Male
Middle Aged
Patella/*physiopathology
*Postoperative Complications/epidemiology/physiopathology
Prospective Studies
Prosthesis Design
Range of Motion, Articular/physiology

Figure

• 

  Fig. 1 (A) The preoperative joint line was defined as a line through the midpoint of the lateral knee joint gap along the perpendicular line to the long axis of the fibula. (B) The postoperative joint line was defined as a line contacting the lowest point of the lateral femoral component along the perpendicular line to the long axis of the fibula. To find out the height of the joint line, we measured the distance from the top of the fibular head to the preoperative and postoperative joint line levels.

• 

  Fig. 2 (A) Patella length-articular ratio on the lateral view; we measured the ratio between patella long length from the superior pole to inferior pole and patella posterior articular length. (B) Patella nonarticular-articular ratio on the lateral view; we measured the ratio between posteroinferior nonarticular length and patella posterior articular length. (C) Patella articular-nonarticular angle on the lateral view; we measured the angle between posteroinferior nonarticular line and posterior articular line. (D) Patella long length and patella inner thickness ratio on the lateral view; we measured patella length as the distance from the superior pole to the inferior pole of the patella and the perpendicular distance from patella length to the posterior articular margin of the patella. (E) Patella inferior pole angle on the lateral view; we measured the angle between patella long length and posteroinferior nonarticular line. (F) Patella facet angle on the Merchant view; we measured the angle between medial and lateral articular margins of the patella. (G) Patella inner thickness ratio on the Merchant view; we measured the ratio between patella long length and perpendicular distance from patella length to the posterior articular margin of the patella.

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  Fig. 3 The mobile bearing post was designed relatively anterior location and long length compared to the fixed bearing post. (A) Lateral aspect of the mobile type bearing. (B) Lateral aspect of the fixed type bearing. a*: anteroposterior distance of the bearing. b†: distance to the post position from the anterior margin of the bearing. c‡: height of the post.

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  Fig. 4 (A) A 76-year-old female patient shows impingement (arrow) between patella bone and bearing post in cruciate-substituting high-flexion total knee arthroplasty. (B) We resected the lower patellar articular part (arrow) when impingement occurred. (C) Impingement disappeared (arrow) after lower patellar articular part resection.

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  Fig. 5 The impingement between the patella bone and the bearing post causes forward displacement of the patella bone and forward displacement of the patella increases as knee flexion increases after impingement. (A) Forward displacement of the patella can lead to stretching of the patellofemoral ligament and retinaculum and reduction of the flexion gap. (B) Therefore, we treated cases with impingement by resection of the lower portion of the patella, and there was no occurrence of forward displacement of the patella.

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