In September 1982, Joanne Hash was referred to Children's Orthopedic Hospital and Medical Center (COH) for intensive physical therapy and surgical release of flexion contractures of the hip and knees caused by the condition polyarticular juvenile rheumatoid arthritis. She suffered a fracture of the left femur during a physical therapy session on October 5, 1982, then sued COH through her guardian ad litem, Toni Hash.
COH moved for summary judgment dismissal of the claim. In support of its motion, COH provided two affidavits from Dr. Carol A. Wallace dated March 20 and May 20, 1985. The plaintiff submitted no affidavits or other evidence in opposition, preferring to argue by memorandum that COH had not met its initial burden because its affidavits were insufficient under CR 56(e). The plaintiff also argued res ipsa loquitur applied and quoted extensively from deposition testimony.
The day before the hearing on the motion, COH filed two *132additional affidavits. In granting COH's motion, however, the court's order specified that only the March 20 and May 20, 1985 affidavits were considered, and did not mention having considered any deposition testimony. Hash appeals; we reverse.
The primary issue in this appeal is whether COH met its initial burden under CR 56. A summary judgment motion should be granted only if the pleadings, affidavits, depositions and admissions on file demonstrate there is no genuine issue as to any material fact, and that the moving party is entitled to judgment as a matter of law. CR 56; Hartley v. State, 103 Wn.2d 768, 774, 698 P.2d 77 (1985).
In resolving that issue, an appellate court engages in the same inquiry as the trial court. Wilson v. Steinbach, 98 Wn.2d 434, 437, 656 P.2d 1030 (1982). A party moving for a summary judgment has an initial burden of showing there are no issues of material fact requiring trial. If the moving party fails to sustain this burden, it is unnecessary for the nonmoving party to submit affidavits or other materials. Graves v. P.J. Taggares Co., 94 Wn.2d 298, 616 P.2d 1223 (1980); Jacobsen v. State, 89 Wn.2d 104, 108, 569 P.2d 1152 (1977). The court must consider all facts submitted and all reasonable inferences from the facts in the light most favorable to the nonmoving party. Wilson, at 437. Moreover, where undisputed facts are reasonably susceptible to more than one interpretation, summary judgment may be improper. Graves, at 303.
Preliminarily, COH contends that Hash's failure to move to strike the hospital's affidavits constitutes a waiver of any deficiencies. To preserve for review a claim that an affidavit is insufficient, a party must register an objection which specifies the deficiency or must move to strike the affidavit before the trial court's entry of summary judgment. Smith v. Showalter, 47 Wn. App. 245, 248, 734 P.2d 928 (1987). Here, since Hash fully argued in her memorandum in opposition to defendant's motion for summary judgment the alleged insufficiencies under CR 56(e) of Dr. Wallace's affidavits, the trial court was fully apprised and *133there was no waiver of the alleged insufficiencies.
The remaining question is: Does an affidavit by an expert medical witness which states only conclusory opinions satisfy the initial burden of the moving party to prove the nonexistence of any material issue of fact? We hold that it does not.
Conclusions of law stated in an affidavit filed in a summary judgment proceeding are improper and should be disregarded. Orion Corp. v. State, 103 Wn.2d 441, 693 P.2d 1369 (1985). Unsupported conclusional statements alone are insufficient to prove the existence or nonexistence of issues of fact. Brown v. Child, 3 Wn. App. 342, 343, 474 P.2d 908 (1970); Mansfield v. Holcomb, 5 Wn. App. 881, 491 P.2d 672 (1971).
It is conceded that Hash sustained a fracture of her left femur during the administration of range of motion exercises at COH. The affidavit of Dr. Wallace, dated March 20, 1985, sets forth a number of conclusions, but does not contain facts relating to, or explaining how, the fracture occurred. Dr. Wallace states in her affidavit that prescribing vigorous physical therapy conforms to the applicable standard of care, and offers the bare conclusion that the physical therapy program prescribed and administered to the plaintiff at COH met that standard of care. Dr. Wallace's affidavit of May 20, 1985, adds the conclusion that a child suffering from juvenile rheumatoid arthritis can suffer a fracture when the therapist is not negligent.
At no point does either affidavit provide this court with a factual description of how the injury occurred. Without that information, a court cannot conclude that there are no material issues of fact to be resolved in deciding the issues of proximate cause and liability. The record is simply deficient. It does not tell us either by facts sworn to under oath or by admissible opinion just how, mechanically, the fracture occurred. The issue of causation is normally a factual issue. Morris v. McNicol, 83 Wn.2d 491, 496, 519 P.2d 7 (1974); Hall v. McDowell, 6 Wn. App. 941, 944, 497 P.2d 596 (1972). Under these circumstances, a summary judg*134ment dismissing the plaintiff's complaint should not be granted.
COH argues that the conclusory opinions stated by Dr. Wallace, even though not supported by specific facts describing the proximate cause of the fracture, are nevertheless sufficient to put the burden on the plaintiff to come forward with a sufficient showing to demonstrate that issues of fact exist.
Under ER 705, an expert witness can testify at trial to an opinion without first stating the factual basis for that opinion. Group Health Coop, of Puget Sound, Inc. v. Department of Rev., 106 Wn.2d 391, 399, 722 P.2d 787 (1986). One can argue, therefore, that the opinion of an expert should be given effect in summary judgment proceedings, even though no supporting facts are included in the expert's affidavit.
We reject that argument for two reasons. First, ER 705 contemplates and makes provision for the opposing party to explore the factual basis for an expert's opinion on cross examination. We have not yet discovered a means for cross-examining an affidavit. Furthermore, without knowledge of the factual basis for the opinion, the court may well be without any means of evaluating the merits of that opinion.
Another reason ER 705 should not be applied literally to affidavits in summary judgment proceedings is the requirement of CR 56(e) that supporting and opposing affidavits set forth admissible facts. While CR 56(e) does not expressly address affidavits of expert witnesses, it does specifically require that:
When a motion for summary judgment is made and supported as provided in this rule, an adverse party may not rest upon the mere allegations or denials of his pleading, but his response, by affidavits or as otherwise provided in this rule, must set forth specific facts showing that there is a genuine issue for trial. . . .
If the adverse party must set forth "specific facts" in order to defeat a motion for summary judgment, elemental *135fairness compels an interpretation of the rule which places the same burden on the moving party if it is to succeed in making the initial showing that there is no material factual issue for trial. One cannot show there is no genuine factual issue without presenting the court with the facts surrounding the critical issues. Here, the critical issue is proximate cause, and COH did not meet that burden.
Expert opinions must be based on the facts of the case and will be disregarded entirely where the factual basis for the opinion is found to be inadequate. Prentice Packing & Storage Co. v. United Pac. Ins. Co., 5 Wn.2d 144, 106 P.2d 314 (1940); Theonnes v. Hazen, 37 Wn. App. 644, 681 P.2d 1284 (1984). In the context of a summary judgment motion, an expert must back up his opinion with specific facts. United States v. Various Slot Machs., 658 F.2d 697, 700 (9th Cir. 1981).
In this case, a child suffered a fracture of her left femur during the administration of physical therapy. Dr. Wallace's affidavit tells us that rheumatoid arthritis causes a demineralization of the bone, therefore making it weaker and more subject to fracture. Dr. Wallace's affidavit also tells us that it is possible for a fracture to occur without the therapist being negligent. We are not told, however, just how, mechanically, the fracture occurred, and without knowledge of the proximate cause of the fracture, summary judgment is improper.
While lesser pressures can fracture a bone weakened by demineralization, the record does not indicate what precautions, if any, are taken to protect a weakened bone during administration of physical therapy. Under these circumstances, we are not satisfied there are no factual issues requiring a trial.
The trial court judgment is reversed and the case remanded for further proceedings consistent with this opinion.
Pekelis, J., concurs.