This study showed satisfactory functional and MR images outcome of microfracture in all 24 studied players. They were all back to play within 18 months despite the fact that the MR images of only 15 players showed "complete healing" scores. The remaining nine had less MRI scores. The decision of allowing subjects to resume full training was taken when clinical examination showed clear evidence of lesion healing, with absence of symptoms, effusion, tenderness, and with a negative compression/rotation test. Therefore, these nine subjects were considered to have the same level of healing as the rest of the subjects. The MR images of these nine subjects showed satisfactory defect filling but with persistence of a subchondral oedema-like signal that lowered their scores. This phenomenon is common after all types of chondral lesion repair [1, 17]. The subjects in this study were competitive athletes, this provides a significant selection bias for the return to play since it has been shown that their return rate for high level athletes is better  and those professional athletes may have a higher rate of return since their motivation is much higher than that for recreational athletes. The return rate of this study can not be extrapolated to recreational athletes, since the personnel and facilities for rehabilitation available to professional players are much better than for the average recreational athlete. In comparison with other repair techniques, the return to play period for microfracture is shorter than for subjects received autologous cartilage transplantation as it was reported by Mithoefer et al. that 87% players maintained their ability to play soccer 52 +/- 8 months postoperatively . A comparison study on 57 young athletes by Gudas et al. showed that 93% of athletes who received autologous osteochondral transplantation and 52% of the athletes who received microfracture returned to sports activities at the pre-injury level at an average of 6.5 months .
This study showed that microfracture produced durable repair tissue in short-term but for how long? Several studies demonstrated the long-term efficacy of microfracture in elite athletes, as well as in traumatic chondral lesions for subjects less than 40 years [3, 4]. Other studies showed that microfracture has good short-term result in the treatment of small cartilage defects and a deterioration in function score starts 18 months after surgery, and the best prognostic factors have young patients with defects on the femoral condyles . The subjects in this study were young with small lesions on femoral condyles which are factors favor them to have long-term repair durability.
Early evidence of lesion healing was seen on MRI as early as three months. By six months 50% of subjects had MRI evidence of complete healing whilst their function scores were normal. Progress of healing as shown by MRI was not always associated with the same degree of functional progress, and vice versa. However, overall the progress shown by MRI and function scores were highly comparable (r2 = 0.993) for the whole period. This study also showed that lesion healing after microfracture is between six to12 months for the majority of subjects. Twenty (83.3%) of the subjects resumed full training and games in this period.
The results revealed a high correlation between MR images and function scores. At six months the strength of association was 99 percent (r2 = 0.993). With progression of healing the strength of association at 12 months was slightly lower 98.6 percent (r2 = 0.986). The strength of association between MR images and function scores at 18 months was again 99 percent (r2 = 0.993). These two non-invasive modalities would be ideal for monitoring healing in daily clinical practice if they proved to be reliable and valid in comparison to the macroscopic healing. The correlation between defect fill shown by MRI and function score at 36 month was reported as 0.84 by Kreuz et al . Mithoefer et al. found that all knee with good fill demonstrated improved knee function and poor fill grade is associated with limited short-term durability .
Brittberg and Winalski  in their evaluation of cartilage injuries and repair found that the subchondral oedema-like signal regresses as the repair site heals, but the precise timeline for the normalization of the marrow signal is unknown. This study showed nine (37.5%) subjects had a persistent subchondral oedema-like signal which extended beyond the period of the study. In a long-term follow-up of microfracture at 36 months, Kreuz et al  also found persistence of marrow oedema in some patients.
The second look arthroscopy was regarded the gold standard for assessing lesion healing in this study, where function scores provided 92 percent (r2 = 0.917) of the information provided by arthroscopy scores, whilst MRI scores provided 89 percent (r2 = 0.894) of the information provided by arthroscopy scores. Both function and MRI scores are indirect assessments of healing. The functional score reflects a subject's condition and MRI provides images for reading. Arthroscopy scores on the other hand, provide direct real time assessments. It is possibly unethical to subject every repaired case to arthroscopy to assess healing so it is promising that both non-invasive modalities showed to provide acceptable alternatives for assessing healing.
It must be stressed that there are no studies comparing microfracture with natural healing and we did not have such control group. Little is known about the natural course of chondral defects, particularly if and when they give clinical symptoms or radiographic signs of deterioration of the knee joint. Therefore, it is not known if any of the treatments that have been recommended for isolated chondral defects alter the natural course of the untreated lesion. No controlled studies have been done to determine whether treatment provides improvement over the natural history of the injury. Thus, scientifically, it is difficult to make a good decision regarding when, or even if, to treat these defects. Subjects with chondral lesions may have periods of time when they are symptomatic followed by times when they can be active without symptoms. The subjects in this study were symptomatic to the extent that they could not perform in their highly demanding sport, and we do believe that microfracture should be regarded as an appropriate treatment option.
In a study by Shelbourne et al  of the outcome of untreated traumatic articular cartilage defects of the knee, they followed 125 anterior cruciate ligament reconstructed patients who had associated chondral defects noticed at the time of reconstruction. They found that the outcome shown by the IKDC score at ten years was similar to that for the control group of ACL reconstructed patients without chondral defects. However, they have not suggested that there are no articular cartilage defects that will benefit from an articular cartilage restoration procedure.
Few studies in the past have discussed the outcome of microfracture by using function and MRI scores simultaneously. Those that did were in mosaicplasty as in the study of Gudas et al [20, 22]. The design and criteria of assessment of those studies were different from this study. Therefore, these made the results we have achieved difficult to assess and compare.