Injuries of the anterior cruciate ligament (ACL) of the knee are common among adults of all ages. Athletes seem to be the primary patient population but they are not alone. Adults of all ages but especially between 20 and 40 are among the most common patients to present with traumatic or degenerative injury of the ACL. Physiotherapists who help rehab these folks are making every effort to find the most optimal postoperative program -- one that will reduce pain and restore function, neuromuscular control, and stability.
In this study from Norway, two types of exercise were compared after ACL reconstruction. The first was a traditional program of strength exercise training. The second was neuromuscular exercise (NE) training. Both programs were carried out for a period of six months. Results were measured for up to two-years, which is much longer than other studies. Most other studies have reported outcomes after only six months.
There's been agreement among researchers that ACL rehab requires two important ingredients in order to regain normal knee function: quadriceps muscle strength and neuromuscular control. The quadriceps muscle is the large muscle along the front of the thigh. It helps straighten the knee and hold it in an extended position. Neuromuscular control is achieved through a combination of physiologic functions within and around the knee. Without neuromuscular control, the knee buckles, twists, or gives way, potentially causing another knee injury (or reinjury of the ACL). Recent research efforts have shown conclusively that neuromuscular training is beneficial following ACL surgery.
The question posed by these physiotherapists was: which program gives the best long-term results -- strength training or neuromuscular exercise? They used a computer program to randomly assign patients to one of these two programs. All patients were adults between the ages of 16 and 40. They all had arthroscopic surgery to reconstruct a torn ACL using a bone-patellar tendon-bone graft. In this technique, a bundle of tendon fibers from the quadriceps muscle as it inserts just below the patella (knee cap) is harvested and used as a donor graft to replace the ruptured ligament.
The rehab programs were conducted on an out-patient basis starting two weeks after surgery and running for six months (two to three times each week). Physiotherapists instructed and supervised each patient throughout the process. Strength-training for the muscles of the leg included progressively increasing repetitions and weights. Targeted muscles were the quadriceps muscle, hamstrings (behind the thigh), gluteus medius (buttock muscle), and gastrocnemius (calf muscle). Stationary biking was used early on to help improve range of motion and decrease joint swelling.
Patients in the neuromuscular training group did balance exercises, exercises to increase dynamic joint stability, and plyometric exercises. Plyometrics helps individuals regain the ability to make sudden changes in direction of movement with speed. The neuromuscular exercise program also included agility drills and specific exercises geared toward individual sports athletes were involved in (e.g., soccer, basketball, volleyball, running). These sports require athletes to make sudden starts and stops as well as quick changes in direction. The knee must be able to do so without hesitation, without pain, and without giving way or wobbling even the slightest bit.
Each program was divided up into phases based on the patient's tolerance, ability to handle increased loads, and time. The neuromuscular exercise program was divided into six phases lasting three to five weeks per phase. The strength-training program was made up of four phases and was directed more by how the patient was doing than by a set amount of time.
Outcome was measured by comparing before and after test results. The Cincinnati knee score of overall knee function measured swelling, giving way, general activity level, walking, stairs, running, and jumping or twisting actions. Pain was measured using the standard Visual Analog Scale (VAS) rating pain as a single number from zero (no pain) to 10 (worst pain). Muscle strength was tested with a specific machine used by physiotherapists called the Cybex 6000. The Cybex is used both to test strength at various speeds and to train muscles (speed and strength).
Another machine called the KT-1000 arthrometer gave the therapists an idea of how stable (stiff) the knees were. And the Short-form 36 questionnaire was used to assess overall mental and physical health. All of these tests are well known in rehab and research. Using them makes it possible to compare one study to another so that results can be compiled for greater statistical analysis.
After following the patients for two full years, they discovered a pattern of differences in the benefits provided by each program. The neuromuscular program had the most benefit in the first year. Patients in this group had better overall knee function and less pain compared with the strength-training group. The strength-training program was more effective in improving knee flexion muscle strength after two years. It really looks like both exercise approaches contribute something a little different at different times in the recovery process. Therefore, both should be used together for the best total results.
This study is important because previous (short-term) studies showing the benefit of neuromuscular training made it seem like that's the direction therapists should go without continuing the more traditional strength-training approach. Without a long-term study to show that both work together over time, changes might have been made in future rehab programs that wouldn't have given patients the best in both short-term and long-term results.
There's no doubt that rehabilitation is key to the success of ACL surgery. Regaining normal function, strength, and motion as quickly as possible after ACL surgery is the goal of most athletes. Strength-training without paying attention to neuromuscular reeducation and vice versa (abandoning strength training in favor of neuromuscular exercise) would be a mistake. It should be noted that not everyone in the study got full function. At the end of the first year, more patients in the neuromuscular group had better overall function. By the end of the second year, the overall functional results were equal between the two groups. The authors suggest future studies combining the two techniques compared with each individual treatment protocol are needed in this ongoing effort to find the best way to optimize ACL rehab.
May Arna Risberg, PT, PhD, and Inger Holm, PT, PhD. The Long-Term Effect of 2 Postoperative Rehabilitation Programs After Anterior Cruciate Ligament Reconstruction. In The American Journal of Sports Medicine. October 2009. Vol. 37. No. 10. Pp. 1958-1966.