The side view of the inside of the knee shows the anterior interval as a mobile gap between fat pad and the front of the tibia. Scarring in this area is called arthrofibrosis.
What is arthrofibrosis?
Arthrofibrosis is internal scarring of the normally mobile soft tissue areas inside a joint following an episode of inflammation.
Commonly the trigger is a knee injury or surgery, often quite minor surgery, where pain inhibits the patient from moving the joint during a critical period of rehabilitation. It can resolve in the early stages with specialist help, but in some cases the patient is left with permanent reduced range of motion, and the kneecap may eventually end up in an abnormally low position (patella baja or infera).
Quick linksArthrofibrosis in the anterior interval
Scarring may involve one or more of the tissue spaces in the knee:
- the large above the kneecap - the suprapatellar pouch
- the space between the fat pad and the patellar tendon - the anterior interval
- the fat pad itself
- the capsular folds at the side of the joint cavity - the lateral gutters (not visible in illustration)
- the capsular gutters at the back of the knee - the posterior capsule
Early in the process, simple adhesions in the anterior interval may be broken with gentle exercise and massage, but later mature scar tissue effectively locks the patellar tendon to the upper part of the tibia, making attempts at flexion very difficult and painful.
The patella becomes tugged down into an abnormally low position (patella infera).
Peer-reviewed papersQuote from peer-reviewed paper:
"....patellofemoral contact forces were significantly increased by simulated adhesions in the suprapatellar pouch and anterior interval....and anterior interval adhesions resulted in a distally translated patella at all flexion angles other than 15° (p < 0.05)...."
Citation: Mikula JD, Slette EL, Dahl KD, Montgomery SR, Dornan GJ, O'Brien L, Turnbull TL, Hackett TR. Intraarticular arthrofibrosis of the knee alters patellofemoral contact biomechanics. J Exp Orthop. 2017 Dec 19;4(1):40. doi: 10.1186/s40634-017-0110-8. PMID: 29260429; PMCID: PMC5736518.
What is the procedure of anterior interval release?
The removal of adhesions and scar tissue is generally known as 'lysis of adhesions', but the procedure of clearing just the anterior interval is called 'anterior interval release'.
The surgeons uses a radiofrequency 'wand' to clear the scar tissue from this area during keyhole surgery (arthroscopy).
Peer-reviewed papersQuotes from peer-reviewed papers:
"The procedure is technically demanding, requiring advanced arthroscopic expertise and accurate portal placement to attain complete lysis of adhesions. In severe cases, minimal flexion at the knee or extensive intercondylar notch scarring and fibrosis may present difficulty in accessing the knee joint in flexion."
Citation: Kukreja M, Kang J, Curry EJ, Li X. Arthroscopic Lysis of Adhesions and Anterior Interval Release With Manipulation Under Anesthesia for Severe Post-traumatic Knee Stiffness: A Simple and Reproducible Step-by-Step Guide. Arthrosc Tech. 2019 Apr 11;8(5):e429-e435. doi: 10.1016/j.eats.2019.01.005. PMID: 31194118; PMCID: PMC6554358.
Quote:
"Adequate analgesia is of prime importance to help the patient match postoperative clinical ROM with intraoperative knee motion. We advise sufficient use of oral pain medications (narcotics and anti-inflammatories) postoperatively. If regional anesthesia is used, use of the indwelling femoral nerve catheter can be continued for a few days for effective local analgesia. PT is started in the hospital on day 1, with the use of a continuous passive motion machine for the first 2 to 3 weeks."
Citation: Kukreja M, Kang J, Curry EJ, Li X. Arthroscopic Lysis of Adhesions and Anterior Interval Release With Manipulation Under Anesthesia for Severe Post-traumatic Knee Stiffness: A Simple and Reproducible Step-by-Step Guide. Arthrosc Tech. 2019 Apr 11;8(5):e429-e435. doi: 10.1016/j.eats.2019.01.005. PMID: 31194118; PMCID: PMC6554358.
Forum discussions
- "ANTERIOR INTERVAL RELEASE How Long pain at site???? help please"
Patients discuss how long pain persists after anterior interval release.