Repair on the femoral condyle of the knee


Autologous Chondrocyte Implantation

Autologous chondrocyte implantation (ACI) is generally indicated for cartilage defects larger than 2 cm² in area. Autologous chondrocyte implantation is a treatment composed of two surgeries. The first is an arthroscopic biopsy (exploratory surgery) to obtain the cartilage cells (chondrocytes). Thereafter, these cells are cultured for a few weeks (4-6). The second intervention, the implantation, involves performing an arthrotomy (open surgical treatment) where the defect is cleaned, a collagen membrane is sewn over the defect and the chondrocytes are then injected therein. Thereafter, the ACI implant must be remodeled and must mature. This lasts at least one year after implantation. The evolution of this process may also influence the timing, intensity and duration of the rehabilitation protocol.

Biomechanics of the tibiofemoral joint

Knowledge of the biomechanics of the tibiofemoral and patellofemoral joint is required to develop rehabilitation protocols following cartilage repair procedures. Without this knowledge, one cannot select exercises likely to cause the least amount of damage. McGinty et al. (2000) recently demonstrated that the tibiofemoral joint has 6 degrees of freedom: flexion/extension with translation, axial rotation with translation and valgus/varus rotation with translation. Flexion and extension in particular play an important role. This movement is actually a combined movement involving rolling and sliding of the joint surfaces (Hambly et al, 2006). When under stress, the femoral condyles roll as a result of increased flexion towards the rear and slide forward, thus shifting the joint towards the rear onto the femoral condyles and the tibial plateau (Reinold et al, 2006).

Knee kinematics is influenced by the cruciate ligaments, muscles and capsular structures. Shearing forces are mainly limited by the cruciate ligaments. Compression forces are generally resisted by the menisci and cartilage.
In the development of this rehabilitation protocol for the ACI procedure, we have tried to select exercises that initially limit shearing forces during peak load and to also take into consideration the size and location of the lesion, as only parts of the femur/tibia move during certain activities.

Rehabilitation phases for cartilage repair after ACI

Two classifications are used in the literature on rehabilitation following cartilage repair procedures. Hambly et al. (2006) use 6 phases based on the biology of healing of the lesion (table 1).

Classification according to Hambly et al. Classification according to Reinhold et al. and Gillogly et al.
Repair and protection (0 – 4 weeks)
Suture of cells, inflammation and proliferation
Proliferation phase (0 – 4/6 weeks)
Protection of the operated region
Inauguration (4 – 8 weeks)
Cell differentiation and start of maturation phase
Transition phase (4 – 12 weeks)
Acquisition of strength in repaired tissue
Maturation (8 – 12 weeks)
Cell differentiation and maturation phase
Remodelling phase (3 – 6 months)
Continued remodelling of the tissue into a more organised structure
Integration (12 – 26 weeks)
Maturation and integration of cells
Remodelling phase (3 – 6 months)
Continued remodelling of the tissue into a more organised structure
Functional adaptation (26 – 52+ weeks)
Maturation and integration of cells
Maturation phase (as from 4 – 6 months)
Tissue reaches complete development
Return to sports (26 – 78+ weeks)
Maturation and integration of cells

Table 1: Comparison between the rehabilitation phases according to Hambly et al. (2006) on one hand and Gillogly et al. (2006) and Reinhold et al. (2006) on the other.

Gillogly et al. (2006) and Reinhold et al. (2006) use 4 phases including a division depending on cartilage development (table 1). A relationship can be drawn from combination of both classifications, as shown in table 1. Until the present, the phases of tissue repair following ACI were based on hypotheses and, thus, this guideline uses a classification involving 7 phases based on achievable goals. The preoperative phase was also added to these 7 phases as a subpart of rehabilitation (table 2).

Rehabilitation protocol

Rehabilitation is individual as each patient recovers differently. Therefore, the following factors should be taken into account when defining an individual rehabilitation program following ACI:

  1. the exact location of the repair (anterior, middle, posterior)
  2. the size of the repair.(<2,5cm²>)
  3. the condition of the borders of the repair, (contained or not contained)
  4. duration of symptoms before surgery (<12months>)
  5. pre-injury activity level (professional/non-professional, competitive/non-competitive, high/low knee impact and high/low training volume),
  6. movement dysfunctions in lower extremity or core.
  7. changes in body mass index


The most important conditions for complete recovery are created during the first 12 weeks of the rehabilitation process. Enclosed is a guideline for rehabilitation. During organisation, the aforementioned principles must be taken into consideration. Strength and functionality can be evaluated at 6, 9, 12 and 24 months after surgery, provided such evaluation is clinically justified (patient experiences no pain or swelling).

Rehabilitation phases General aims
1 Preoperative phase Education for rehabilitation planning
Stress of unaffected zones
2 0 – 6 weeks post surgery Repair to complete ROM (range of motion) for defects < 5.0 cm²
Achievement of homeostasis (no swelling or pain) in joint
3 4 – 12 weeks post surgerye Achievement of normal pattern of movement (muscle control)
4 10 – 26 weeks post surgery Building of specific strength within the safe zones
Maximising of condition through low impact* activities (rowing and biking) or arm activities
5 5 – 9 months post surgery

Depending on the size of the repair, slow or rapid extension
Muscle control within repaired zone
Isometric control under high load in repaired zone
Eccentric control:

  • Full range during low impact
  • High impact** within safe zones
6 9 – 12 months post surgery Sport-specific exercises for low impact sport allowed (no pivoting sports and open skills)
High impact sports not allowed
7 > 12 months post surgery Sport-specific exercises for high impact sports
Low impact sport exercis

Table 2: Rehabilitation phases in relation to rehabilitation aims - * low impact: rowing and biking - ** high impact: pivoting sports, jogging, etc.

Recommended literature

  1. Gillogly, SC, TH Myers & MM Reinold (2006). Treatment of full-thickness chondral defects in the knee with autologous chondrocyte implantation. J. Orthop Sports Phys Ther, 36(10), 751 – 764.
  2. Hambly, K, V Bobic, B Wondrasch, D van Assche & S Marlovits (2006). Autologous chondrocyte implantation postoperative care and rehabilitation. Am J Sports Med, 34(6), 1020 – 1038
  3. Jong de, SN, DR van Caspel, MJ van Haeff & DBF Saris (2007). Functional assessment and muscle strength before and after reconstruction of chronic anterior cruciate ligament lesions. Arthroscopy, 23(1), 21-28, 28.e1-3.
  4. Reinold, MM, KE Wilk, LC Macrina, JR Dugas & EL Cain (2006). Current concepts in the rehabilitation following articular cartilage repair procedures in the knee. J Orthop Sports Phys Ther, 36(10), 774 – 794.
  5. McGinty G, Irrgang JJ, Pezzullo D. (2000). Biomechanical considerations for rehabilitation of the knee. Clin Biomech 15(3):160-6.
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