rupture of the anterior cruciate ligament ( acl ) is the most common injury of the knee requiring surgical treatment .
while a conservative treatment approach leads to satisfactory results in a population that places low demand on the knee joint [ 31 , 41 ] , persisting instability prevents patients from participating in activities that require high levels of joint pivoting , such as soccer and skiing .
today s gold standard in acl repair was developed by brckner in 1966 and uses the middle third of the patellar ligament as transplant to restore knee joint stability .
although arthroscopic techniques have improved tremendously since then , and current acl reconstruction techniques are an excellent option for restoring sagittal plane stability of the knee , the clinical results with tendon grafts are still under discussion . despite numerous publications reporting good - to - excellent results , the meta - analysis of biau et al .   revealed that only 40  % of patients achieve full recovery independent of surgical technique .
one explanation could be that removal of the native acl tissue containing sensory nerve fibres causes the ligament to lose its function within the joint s  proprioceptive envelope [ 3 , 23 ] , thus impairing muscular stabilization of the knee .
based on this theory , the authors started to investigate a strategy for preserving the torn acl in 2007 .
this can be partly explained by biological factors such as cell deficiencies , alterations in cellular metabolism , the hostile environment of the synovial fluid [ 12 , 42 ] , and the lack of blood supply [ 2 , 26 ] .
moreover , the postinjury instability does not allow the torn ligament to heal . while recent studies support the potential of biological self - healing for the ruptured acl [ 34 , 35 , 38 ] , the persisting postinjury translation in the antero - posterior plane separates the ligament stumps by 510  mm and prevents possible self - healing and formation of stable scar tissue [ 1 , 16 , 43 ]
. to address this problem , a new technique was developed , dynamic intraligamentary stabilization ( dis ) , hypothesizing that continuous posttraumatic stabilization of the knee can enable mechanically stable acl healing .
encouraged by the success of dis in a sheep model , the technique was applied in a series of 10 physically active individuals with a torn acl .
inclusion criteria were an acl rupture not older than 14  days , patient age < 45  years , no previous surgery on the injured knee , and regular participation in sports requiring pivoting of the knee joint .
ten consecutive patients ( eight males , two females ) met the inclusion criteria and underwent surgery between august 2009 and february 2010 .
median age was 25.4  years ( range 1941  years ) ; the right / left knee ratio was 7/3 .
the median accident - surgery interval was 9.9  days ( range 213  days ) .
the rupture was located in the middle third of the ligament in seven patients and in the proximal third in three patients .
each patient was placed in a supine position with the knee positioned in a static knee holder with a tourniquet inflated to 350  mm hg .
an antero - lateral portal was used for the camera and an antero - medial portal for the instruments .
removal of too much tissue , especially from the inferior part of the fat pad , was avoided to preserve nutritional arteries to the acl passing through this area .
the tibial footprint of the acl was marked using an intra - articular guide , and a wire was passed through the tibia to this point .
a 10.5-mm threaded sleeve ( mathys ltd , bettlach , switzerland ) was then inserted into the tibia .
a suture passer was inserted through the screw into the distal acl stump , and a preliminary thread was passed through the ligament .
the femoral footprint was identified using a guide from the antero - medial portal , and a wire was passed at 120 degrees of flexion to the lateral aspect of the femur .
the wire was passed through the skin , and the definitive polyethylene wire was inserted from the antero - lateral femoral position to the antero - medial aspect of the tibia .
a metallic spring was inserted in the screw , and the polyethylene wire was fixed with a cover at the end of the screw at a tension of 80  n. the dis technique holds the knee in a fixed posterior translation at every degree of flexion , ensuring that the two ligament stumps are kept as close to each other as possible at all times ( fig .  1 ) .
the surgery was then completed by microfracturing of the femoral footprint and induction of a leucocyte- and platelet - rich fibrin ( l - prf ) clot at the rupture site.fig . 
1dynamic screw - spring mechanism pushes the tibia into a posterior translation at every degree of flexion dynamic screw - spring mechanism pushes the tibia into a posterior translation at every degree of flexion postoperative treatment consisted of the patient spending 3  days in a fixed position with the knee fully extended .
the leg was then loaded with 15  kg of weight for 3  weeks and mobilized without any flexion limitations .
beginning at 4  weeks postoperative , the leg was loaded with full body weight and reinforcement training of the quadriceps and hamstrings was initiated using closed chain knee exercises . intensive proprioceptive training was initiated with a trampoline and balancing exercises on an unstable board . running was allowed after 6  weeks and pivoting sports after 3  months .
all patients were evaluated according to a prospective protocol , 6  weeks , 3 , 6 , 12 , and 24  months after surgery .
the following instruments were used for outcomes assessment at each follow - up : tegner score , lysholm score , the international knee documentation committee ( ikdc ) score , and visual analogue scale ( vas ) for assessment of patient satisfaction ( 0  =  completely dissatisfied , 10  =  completely satisfied ) .
knee laxity was assessed by measuring anterior translation at 30 degrees flexion using a rolimeter ( aircast , neubeuern , germany ) and comparing it with the contralateral knee .
all patients were informed that their treatment would involve a completely new technique , to which they gave voluntary written informed consent ( cantonal ethics committee of berne , switzerland : ref .- nr .
conventional radiographic evaluation was performed immediately after surgery and at the 6-week and 12-month follow - ups .
mri investigations were conducted 6  weeks , 3 , 6 , and 12  months after the intervention using an advanced 3 tesla scanner ( magnetom verio ; siemens , erlangen , germany ) with a dedicated 15-channel knee coil .
all examinations were reported in random order by a specialized radiologist with a more than 15-years experience in musculoskeletal radiology .
the radiologist was blinded to all clinical information except for the surgical repair of the acl .
first , image quality was assessed using a 5-point scale ( 5  =  optimal image quality , 4  =  very good image quality , 3  =  diagnostic image quality , 2  =  anatomic structures only identified , 1  =  anatomic structures not seen ) .
next , the mris were examined for intactness of the ligament by an independent evaluator applying the following criteria : the ligament tear was rated in three grades similar to those used by khne et al .  
after acl repair , grade 3 representing a non - delineated ligament , grade 2 a wavy but continuous ligament contour , and grade 1 a continuous ligament . the 4-level grading system for the pcl , as proposed by howell et al .
, was adapted to analyse variations in the signal intensity parameters of the graft . in grade
i , a homogeneous , low - intensity signal was observed within the entire graft segment . in grade ii , at least 50  % of the  normal ligament signal was observed . in grade iii ,
the graft segment depicted less than 50  % of the normal ligament signal . in grade iv
, there was a diffuse increase in signal intensity with abnormal ligament strands . to express the variability and distribution of the underlying data , the median values of outcome scores and their range
no inferential statistics were used in this exploratory descriptive study ( n  =  10 ) .
the ligament tear was rated in three grades similar to those used by khne et al .  
after acl repair , grade 3 representing a non - delineated ligament , grade 2 a wavy but continuous ligament contour , and grade 1 a continuous ligament .
the 4-level grading system for the pcl , as proposed by howell et al . , was adapted to analyse variations in the signal intensity parameters of the graft . in grade
i , a homogeneous , low - intensity signal was observed within the entire graft segment . in grade ii , at least 50  % of the  normal ligament signal was observed . in grade iii ,
the graft segment depicted less than 50  % of the normal ligament signal . in grade iv
to express the variability and distribution of the underlying data , the median values of outcome scores and their range were calculated and reported .
no inferential statistics were used in this exploratory descriptive study ( n  =  10 ) .
at 5  months after surgery , patient number 6 ( a 24-year - old male sports student ) suffered from a re - rupture after sustaining a direct rotation trauma playing soccer . until then
, the patient had been pain - free with a lysholm score of 97 and a tegner score of 5 at the 3  month follow - up .
6  weeks after the second trauma his completely ruptured acl was replaced by a bone - tendon - bone ( btb ) graft .
the remaining nine patients were all monitored according to the clinical follow - up protocol and had a complete set of mri investigations .
the lysholm score was 100 before injury , 99 ( 97100 ) after 3  months , and 100 after 24  months .
the ikdc score reached 98 ( 97100 ) after 24  months , and with six points the group`s median tegner activity score remained the same as before the accident .
after 3  months , the anterior translation difference was 0.5  mm ( 3 to 3 ) compared with the contralateral side and 1.4  mm ( 1 to 3 ) after 24  months . before surgery
, it was 4.9 ( range 37  mm , sd 1.2  mm ) .
the anterior stop was hard in three patients and semi - hard in six patients .
median patient satisfaction was 9.5 ( 810 ) after 3  months and 9.8 ( 910 ) after 24  months ( table  1).table  1clinical scores at follow - up examinations ( median values and range)scores / testsbefore injury3 months6 months12 months24 monthslysholm10099.1 ( 97100)99.8 ( 99100)99.8 ( 98100)100ikdc10092.1 ( 8796)94 ( 9098)97.8 ( 97100)98 ( 97100)tegner6 ( 49)5 ( 46)5 ( 48)6 ( 59)6 ( 59) lachmann ( mm)0.5 ( 33)1.0 ( 33)1.2 ( 23)1.4 ( 13)pat .
( 810)9.6 ( 910)9.8 ( 910)9.8 ( 910 ) clinical scores at follow - up examinations ( median values and range ) imaging quality was rated as optimal ( score 5 ) in nine patients and very good ( score 4 ) in one patient at 6  weeks .
metal artefacts obscured 18  % of the distal acl ( range 1223  % ) but did not alter the morphology of the proximal and middle third of the ligament .
all repairs were well defined , and ligament continuity was fully restored . applying the howell grading system ,
mri signals were rated i in 2 of the 10 patients after 6  weeks and ii in the remaining 8 patients .
after 3  months and for all later assessments , the signals were rated i for all patients except patient number 6 after the second rupture of his ligament ( fig . 
2lateral mri showing the torn acl immediately after injury and at 12  months follow - up ( after removal of screw ) lateral mri showing the torn acl immediately after injury and at 12  months follow - up ( after removal of screw )
imaging quality was rated as optimal ( score 5 ) in nine patients and very good ( score 4 ) in one patient at 6  weeks .
metal artefacts obscured 18  % of the distal acl ( range 1223  % ) but did not alter the morphology of the proximal and middle third of the ligament .
patient number 6 was also rated grade a before his re - rupture . all repairs
were well defined , and ligament continuity was fully restored . applying the howell grading system ,
mri signals were rated i in 2 of the 10 patients after 6  weeks and ii in the remaining 8 patients .
after 3  months and for all later assessments , the signals were rated i for all patients except patient number 6 after the second rupture of his ligament ( fig . 
2lateral mri showing the torn acl immediately after injury and at 12  months follow - up ( after removal of screw ) lateral mri showing the torn acl immediately after injury and at 12  months follow - up ( after removal of screw )
the most important finding of the present study was that a dynamic intraligamentary stabilization of the knee with a freshly ruptured acl in combination with biological improvement of the healing environment can lead to a biomechanically stable acl with good functional scores and high patient satisfaction .
acl rupture is a devastating knee injury that is associated with a significant risk of developing osteoarthritis .
controversially , this risk is reported to be even higher in patients undergoing surgical stabilization of the acl [ 11 , 25 , 29 ] .
these problems may be attributable to loss of proprioception after complete removal of the acl [ 5 , 31 , 37 ] as well as to insufficient restoration of the three - dimensional stability of the knee [ 6 , 36 , 39 ] .
it was therefore hypothesized that conservation of the native acl tissue is necessary to preserve proprioception and restore the individual three - dimensional anatomy of the ligament .
the paradigm that a torn acl has insufficient healing capacity and must be replaced by a tendon graft remains prevalent [ 14 , 20 ] . opposing this paradigm ,
a series of publications have indicated that under certain circumstances the injured acl can produce a stable scar .
reported a better clinical outcome and improved stability with suturing the acl and augmenting the tissue with polydioxanone than with acl replacement .
steadman et al .   described a method known as the  healing response wherein placement of undifferentiated stem cells into the rupture zone induced stable healing of the torn acl in an athletically active , skeletally immature patient . in 2002 , fujimoto et al .  
published the results of 31 acl ruptures in patients with low athletic demands treated conservatively for 23  months with an extension block soft brace without anterior stabilization : 23 knees ( 74  % ) were stable with a continuous acl on mri at final follow - up .
boldrini et al .   reported stable healing in 26 athletes with an incomplete acl tear using primary sutures in combination with bone marrow stimulation .
the literature to date indicates that stability and biology are the two main determinants for acl healing .
every tissue demands a certain level of stability to heal , but since a knee with an injured acl shows a significant increase in antero - posterior translation of the tibio - femoral joint , normal knee movements result in a constant disconnection of the two acl stumps , creating an unstable healing environment
. the published method of knee bracing in a constant posterior translation for 3  months has already produced a remarkable number of healed ligaments , but it is not widely accepted because of the discomfort it causes [ 17 , 22 ] .
the authors have developed a new technique called dynamic intraligamentary stabilization ( dis ) that restores the intrinsic stability of the knee with minimal discomfort for the patient .
the dis device employs an internal screw - spring mechanism that acts as a dynamic internal fixator which pushes the knee into a maximum posterior translation in any degree of flexion .
the spring is also functional when the intraligamentary thread is not placed in an isometric position .
this technique has already been shown to provide sufficient mechanical stability to enable biomechanically stable healing of the acl in a sheep model .
recent studies have demonstrated that introduction of a collagen - platelet composite into a transected acl can significantly increase its healing capacity [ 30 , 32 , 33 ] .
used a collagen - platelet composite to bridge the wound site and reported healing with recovery of over 50  % of the initial ligament strength after 4  weeks .
[ 44 , 45 ] have demonstrated that solid scaffolds can be used for long - term ( up to 28  days ) delivery of growth factors ; in particular , l - prf can be used as a regenerative in situ tissue engineering method during treatment of acl injuries .
this technique was adapted in combination with microfracturing according to steadman to optimize the biological healing capacity of the acl .
the mri investigations at 3 , 6 , and 12  months showed a continuous increase in scar tissue as represented by fibres of low signal intensity .
in addition , clear remodelling of the ligament was detectable at 6  months , and the independent evaluator judged the continuity of the ligaments as restored .
furthermore , the dynamic aspect of the repair resulted in a straight appearance of the fibre bundles without the wavelike morphology observed with other surgical techniques .
clinically , all patients exhibited practically normal knee function after 1  year with a lysholm score of almost 100 and an ikdc score of 98 . these results are strikingly improved in comparison with the outcome after conventional acl repair with a tendon graft . however
, the reported ceiling effects of the lysholm score need to be considered in this series of highly motivated and active patients .
a better discriminating outcome instrument may be needed for these types of patients in the future . in their meta - analysis ,
biau et al .   reported that only about 40  % of patients made a full recovery after acl reconstruction , with only 33  % having a normal ikdc score after a semitendinosus transplant and 41  % having a normal ikdc after a btb ( ligamentum patellae ) transplant .
thus , more than 60  % of patients ( 708 of 1,125 for the two reconstruction groups ) did not fully recover ( final overall ikdc score class a ) after reconstruction .
the present authors attribute the excellent clinical results of their new technique to the restored stability of the knee on one hand , but even more to the preservation of the acl tissue , which allows for the restoration of a physiological proprioception .
barret points out that ligament tests and knee scores correlate poorly with patient satisfaction scores , but proprioception is a major factor in measuring the overall outcome of acl reconstruction .
patients in the present study reported a satisfaction of 9.8 on vas after 1  year , indicating that healing of the acl tissue may restore not only the three - dimensional stability of the knee but also the physiological proprioceptive envelope .
casteleyn states that the real benchmark of success in the treatment of acl ruptures has to be the avoidance of treatment morbidity , secondary surgery , and osteoarthritis . in the meta - analysis of biau
et al . , 1322  % of the patients complained of persisting knee pain , mainly associated with donor - site morbidity .
the sample size is small , there is no control group , and the follow - up is not long enough to address posttraumatic arthritis , which results in an evidence level of only iv .
the authors conclude that this study could revitalize the discussion of preserving the torn ligament .
it could be an additional option between the conservative treatment and the replacement of the acl .
dynamic intraligamentary stabilization in combination with l - prf and microfracturing of the notch can lead to stable clinical and radiological healing of the torn acl after 1  year .
patients exhibited normal knee function reported excellent satisfaction and were able to return to their previous levels of sporting activity .
the present findings support the discussion of a new paradigm in acl treatment based on preservation and self - healing of the torn ligament .
 purposereplacement of the torn anterior cruciate ligament ( acl ) with a transplant is today`s gold standard . 
 a new technique for preserving and healing the torn acl is presented . 
 hypothesis : a dynamic intraligamentary stabilization ( dis ) that provides continuous postinjury stability of the knee and acl in combination with biological improvement of the healing environment [ leucocyte- and platelet - rich fibrin ( l - prf ) and microfracturing ] should enable biomechanically stable acl self-healing.methodsten sportive patients were treated by dis employing an internal stabilizer to keep the unstable knee in a posterior translation , combined with microfracturing and platelet - rich fibrin induction at the rupture site to promote self - healing . 
 postoperative clinical [ tegner , lysholm , international knee documentation committee ( ikdc ) , visual analogue scale patient satisfaction score ] and radiological evaluation , as well as assessment of knee laxity was performed at 6  weeks , 3 , 6 , 12 , and 24  months.resultsone patient had a re - rupture 5  months postoperative and was hence excluded from further follow - ups . 
 the other nine patients presented the following outcomes at 24  months : median lysholm score of 100 ; ikdc score of 98 ( 97100 ) ; median tegner score of 6 ( range 95 ) ; anterior translation difference of 1.4  mm ( 1 to 3  mm ) ; median satisfaction score of 9.8 ( 910 ) . 
 mri showed scarring and continuity of the ligament in all patients.conclusionsdis combined with microfracturing and l - prf resulted in stable clinical and radiological healing of the torn acl in all but one patient of this first series . 
 they attained normal knee scores , reported excellent satisfaction and could return to their previous levels of sporting activity.level of evidencecase series with no comparison group , level iv . 
Level of evidence
Introduction
Materials and methods
Surgical technique
Clinical evaluation
Radiological evaluation
Morphology and continuity
Signal intensity
Statistical analysis
Results
MRI
Discussion
Conclusion
Conflict of interest