Research Review by Dr. Shawn Thistle©


Feb. 2008

Study Title:

A comprehensive rehabilitation program with quadriceps strengthening in closed versus open kinetic chain exercise in patients with anterior cruciate ligament deficiency: A randomized clinical trial evaluating dynamic tibial translation and muscle function


Tagesson S, Öberg B, Good L, Kvist J
Authors’ Affiliations: Divisions of Physiotherapy, Orthopedics/Sports Medicine, and Clinical and Experimental Medicine, Linköpings Universitet, Linköpings Sweden.

Publication Information:

American Journal of Sports Medicine 2008; 36(2): 298-307.


After an injury to the anterior cruciate ligament (ACL) of the knee, the primary goal of rehabilitation is to restore normal knee function and neuromuscular control. The major components of this objective include rehabilitating muscle strength, proprioception, coordination, and tissue health. One challenge of particular importance in ACL injury rehabilitation is to adequately strengthen the quadriceps. Existing literature suggests that many ACL patients experience continued quadriceps weakness, which has been shown to correlate with poor function after injury.

From a training and rehabilitation perspective, quadriceps strengthening can be achieved in two different ways:
  1. Open Kinetic Chain (OKC): isolate one joint of the kinetic chain with the distal segment free to move (ex. seated leg extension)
  2. Closed Kinetic Chain (CKC): modeled as single linkages, movement in one joint causes simultaneous movement in other joints of the limb (normally with the distal part of the limb planted – ex. squat)
It is generally accepted that CKC exercises are safer than OKC exercises, as they produce lower amounts of anterior shear forces (particularly in the final 30° of extension), and hence they normally form the majority of exercises in an ACL rehabilitation program. Clinical studies have suggested that OCK exercises result in higher anterior tibial translation when compared to CKC exercises, although this tenet is somewhat controversial. Despite this, some clinicians argue that OKC exercises have a role to play, as they do activate and stress the quadriceps considerably.

Patients with ACL deficiency have diminished capacity to withstand anterior shear at the knee joint, with potential for further injury due to increased tension on secondary stabilizers. Thus the question of OCK vs. CKC exercises becomes important, particularly in terms of anterior translation and functional clinical outcomes. Therefore, the aim of this study was to compare the efficacy of a comprehensive rehabilitation program for patients with ACL insufficiency supplemented with either OCK or CKC exercises, on static and dynamic sagittal tibial translation, subjective knee function, and muscle function.

42 patients were randomly assigned to one of two treatment groups (see below) if they met the following inclusion criteria: age between 15-45, with a diagnosis of a unilateral ACL rupture that was no more than 14 weeks old (NOTE: all ACL injuries were verified by MRI imaging and/or arthroscopy). Exclusion criteria included:
  • additional injury to the lower extremity
  • previous surgery to the lower extremity
  • Exceptions: partial injury to the medial meniscus or minor medial collateral ligament injury in the ipsi- or contralateral knee
Treatment Groups:
  1. OCK Group (n = 22): the unique exercises utilized were seated knee extension, as well as standing hip extension
  2. CKC Group (n = 20): the exercise unique to this group was the 1-legged squat (which also served to load the hip extensors)
Each treatment group underwent an identical rehabilitation program aside from the above mentioned exercises, in the following phases:
  1. PHASE 1: protection (weeks 1-4)
  2. PHASE 2: early strength training (weeks 5-8)
  3. PHASE 3: intensive strength training (weeks 9-12)
  4. PHASE 4: intensive strength training and return to sports
Activities included in the program:
  • bicycle, running and cross trainer – progressed as tolerated
  • straight leg raise
  • 2-leg Swissball wall squats
  • 20 cm step-ups
  • variety of balance exercises
  • hip ab/adduction
  • heel raise
  • 1-leg curl
  • lunges
  • slide board
  • 2-leg lateral jumps
  • agility drills and sport-specific activities
Strength exercises were started at 50-60% of 1 repetition maximum (1RM = as determined with the healthy leg) and progressed 70-80% 1RM throughout the phases.

Outcomes were measured at baseline and after 4 months of rehabilitation, and included:
  • passive and active knee ROM
  • joint swelling measured as mid-patella knee joint circumference
  • instrumented Lachman test (CA-4000, OSI Inc., Haywood, California) with the knee in 20° flexion – average of three values using both 90N and 134N of force
  • gait testing with a Kistler Force Plate to measure dynamic anterior translation
  • surface EMG recording (normalized by MVC of non-injured leg) of activity in the vastus medialis, vastus lateralis, hamstrings, lateral gastrocnemius, and gluteus maximus
  • subjective knee function was measured with The Lysham Score and the Knee Osteoarthritis Outcome Score (KOOS)
Pertinent results of this study include:
  • there were no significant between-group differences in joint swelling and passive ROM in the injured knees after rehabilitation, despite both groups having significant swelling and passive ROM limitations before rehab (p < 0.05)
  • Lachman test results were not significantly different for maximal tibial translation between groups for the uninjured leg, injured leg, and the ratio of injured:uninjured before and after rehab
  • there were no significant differences in tibial translation during gait between groups, before or after rehab
  • muscle activation was similar in both groups before and after rehab (p < 0.001)
  • isokinetic strength of the quadriceps in the injured leg (presented as a % of the uninjured leg maximum) was significantly greater in the OKC group compared to the CKC group (p < 0.009) after rehab (note: no hamstring differences were noted)
  • in optimally compliant subjects, the above difference in strength was even greater

Conclusions & Practical Application:

This study demonstrated that a comprehensive rehabilitation program supplemented with OKC quadriceps exercise can lead to greater improvements in quadriceps strength compared to a similar program with CKC exercises. It should be emphasized here that both protocols were effective, with no differences noted in anterior tibial translation (statically or dynamically), hamstring strength, and functional outcomes.

This study was limited by a relatively small sample size, poorly defined initial level of injury, low compliance in some subjects, and potential for confounding among the exercises included in the standard program. To elaborate, each group performed Swissball squats and lunges, two CKC exercises. It could therefore be argues that the OKC group did do some CKC exercises, which may cloud the results somewhat. That being said, the significant increase in quadriceps strength in the OKC group in the absence of any untoward effects suggests that OKC exercises may have a role to play in ACL rehab…this should be the take home message from this study. Further research is required.